DMQ A12V-U112 Assembly instructions

Hardware Installation Manual
Modular Silicon Expansion Valve (MSEV)
High Capacity Modular Silicon Expansion Valve (HC-MSEV)
Very High Capacity Modular Silicon Expansion Valve (VHC-MSEV)
Universal SuperHeat Controller/Sensor (USHX)
Revision 1.7
DunAn Microstaq, Inc.
4120 Freidrich Lane, Suite 225
Austin, Texas 78744 United States
[phone]
www.dmq-us.com
Published: July 2019
©2019

This manual is applicable to the following MSEV model numbers:
A12V-U112
A12V-U116
A12V-U118
A12V-U120
A12V-U124
A12V-C112
A12V-C116
A12V-C119
A12V-C122
A12V-C124
A12V-C127
A12V-C132
A12V-C134
A24V-U112
A24V-U116
A24V-U118
A24V-U120
A24V-U124
A24V-C112
A24V-C116
A24V-C119
A24V-C122
A24V-C124
A24V-C127
A24V-C132
A24V-C134
This manual is applicable to the following HC-MSEV model numbers:
A12V-C332
A12V-C338
A12V-C343
A12V-C348
A12V-C352
A12V-C355
A12V-C358
A24V-C332
A24V-C338
A24V-C343
A24V-C348
A24V-C352
A24V-C355
A24V-C358
This manual is applicable to the following VHC-MSEV model numbers:
A12V-C6612
A12V-C6650
A12V-C6715
A12V-C6773
A12V-C6799
A24V-C6612
A24V-C6650
A24V-C6715
A24V-C6773
A24V-C6799
This manual is applicable to the following USHX model numbers:
USHC-G1.3b-BAAAXXX
USHS-G1.3b-BAAAXXX
Additional Product Markings for USHC-G1.3b and USHS-G1.3b
Operating Control
Independently Mounted
Pollution Degree 2
Impulse Voltage: 300 V
SELV Circuit Voltage I/O
Operating Pressure: 21 to 240 psia
Proof Pressure: 600 psi
Burst Pressure: 1500 psi

Table of Contents
1Before You Begin ....................................................................................................................1
1.1 About This Manual.................................................................................................................... 1
1.2 Document Conventions ............................................................................................................ 1
1.3 Acronyms ..................................................................................................................................1
1.4 About the MSEV Series and the USHX ......................................................................................2
2Mechanical Installation ...........................................................................................................4
2.1 Installing a MSEV Series Valve .................................................................................................. 4
2.2 Installing the USHX.................................................................................................................... 6
3Electrical Wiring....................................................................................................................10
3.1 Single USHC and MSEV Series Valve or Single USHS...............................................................10
3.2 Multiple USHCs and MSEV Series Valves or Multiple USHSs ..................................................12
4 Troubleshooting .....................................................................................................................17

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
1Before You Begin
1.1 About This Manual
The following table shows a summary of the sections in this document and their descriptions.
Table 1-1 Descriptions of the Sections in the Document
Section Title
Description
Before You Begin
This section provides preliminary information about the products.
Mechanical Installation
This section provides instructions about the mechanical installation
of the MSEV series and the USHX in the system.
Electrical Wiring
This section provides instructions about the electrical wiring of the
MSEV series valve and the USHX.
Troubleshooting
This section provides solutions to potential problems.
1.2 Document Conventions
The following table shows a list of symbols found in this document and their descriptions.
Table 1-2 Descriptions of Symbols in the Document
Symbol
Description
WARNINGS indicate that the action you are taking could either
cause injury to yourself or could harm your products and systems.
IMPORTANT NOTES appear in the text to indicate additional
information that should be noted.
1.3 Acronyms
The following table shows a list of acronyms used in this document.
Table 1-3 Acronyms and Abbreviations in the Document
Acronym
Description
MSEV
Modular Silicon Expansion Valve
HC-MSEV
High Capacity Modular Silicon Expansion Valve
VHC-MSEV
Very High Capacity Modular Silicon Expansion Valve
MSEV Series
MSEV, HC-MSEV and VHC-MSEV
MEMS
Microelectromechanical Systems
EEV
Electronic Expansion Valve
TXV
Thermostatic Expansion Valve
HVAC/R
Heating, Ventilation, Air Conditioning, and Refrigeration
USHX
Universal SuperHeat Controller or Sensor
USHC
Universal SuperHeat Controller
USHS
Universal SuperHeat Sensor
ID / OD
Inner Diameter / Outer Diameter
AC / DC
Alternating Current / Direct Current

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
1.4 About the MSEV Series and the USHX
The MSEV series valves Modular Silicon Expansion Valve (MSEV), High Capacity Modular Silicon
Expansion Valve (HC-MSEV) and the Very High Capacity Modular Silicon Expansion Valve (VHC-MSEV),
shown in Error! Reference source not found., are two-stage proportional control expansion valves that
utilize DunAn Microstaq’s patented silQflo® technology. The silQflo is a microelectromechanical systems
(MEMS) microvalve technology used to provide precise mass flow control for industry-standard HVAC and
refrigeration applications. The MSEV consists of a MEMS pilot valve which acts as a first stage valve that
applies varying fractions of fluid line pressure onto the second stage spool valve according to the
command signal provided by the Universal SuperHeat Controller (USHC). The MSEV is installed at the inlet
of the evaporator.
Figure 1-1 MSEV Family
The Universal SuperHeat Controller/Sensor (USHX), shown in Figure 1-2, is offered either as a:
a. Universal SuperHeat Controller (USHC): To drive and control a MSEV series valve.
b. Universal SuperHeat Sensor (USHS): To measure and report temperature, pressure, and
superheat values.
The USHX consists of an internal MEMS pressure sensor and a processing unit. It uses a wiring harness,
shown in Figure 1-3, to measure the evaporator temperature and control a MSEV series valve.The USHX
is installed at the outlet of the evaporator; it mounts on a ¼” access fitting and utilizes the Modbus RTU
communication protocol for user interaction.
Figure 1-2 USHX Wiring Harness
Figure 1-3 USHX

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
The USHX and its wiring harness pin assignments are shown in Table 1-4.
Table 1-4 USHX and Wiring Harness Pin Assignments
USHX-G1.3b Series Model Numbers
USHC-G1.3b-BAAAXXX
USHS-G1.3b-BAAAXXX
Pin Number
Pin Name
Pin Function
Type of Wire
Wiring Harness Model
WH-USHX-AX
Pin 1
AC2
Power Input
Red, 18 AWG

Pin 6
AC1
Power Input
Black, 18 AWG

Pin 3
DATA-
RS485- Communication
Black, 24 AWG,
Shielded

Pin 4
DATA+
RS485+ Communication
Red, 24 AWG, Shielded

Pin 2
DGND
Digital Signal Ground and
Thermistor Signal Ground
Green, 22 AWG

Pin 9
SENS
Thermistor Power
Black, 24 AWG

Pin 7
PWM+
PWM Output
White, 18 AWG

Pin 8
PWM-
PWM Output
White, 18 AWG

Pin 5
GPB
General Purpose –Not
Utilized
Brown, 20 AWG

Pin 10
GPA
General Purpose –Not
Utilized
Purple, 20 AWG

Note:
= Available

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
2Mechanical Installation
This section describes the mechanical installation of a MSEV series valve and USHX. Figure 2-1 below
shows an example of a typical system where the MSEV series valve and USHX devices would be integrated
into. Like conventional thermostatic expansion valves (TXVs) or electronic expansion valves (EEVs), the
MSEV series valve is installed at the inlet of the evaporator. The USHC, which drives and controls the MSEV
series valve, is installed at the outlet of the evaporator, in place of the TXV bulb or EEV controller sensing
device. The MSEV series and USHC are connected together by a wiring harness. A thermistor at the outlet
of the evaporator measures the temperature, and the USHC is powered by the Class 2 power source.
Do NOT turn the power source ON until installation of MSEV series valve, USHX and
wiring harness is complete. For the user’s own safety, only Class 2 power source
should be used to power the MSEV series and USHX devices.
Figure 2-1 MSEV series valve and USHC installation schematic
2.1 Installing a MSEV Series Valve
To install the MSEV series valve, complete the following steps:
1. Pump down and recover any residual refrigerant from the system.
2. Remove the current TXV and its bulb or EEV and its controller by cutting. Take care to minimize
the risk of introducing contaminates into the system when removing the existing valve.
3. Before continuing, clean the copper connections of the MSEV series valve. The OD of the MSEV,
HC-MSEV and VHC-MSEV copper tubes are 3/8”, 5/8” and 3/4” respectively.
Do NOT reduce the length of the copper tubes when brazing.
Flare fittings should be used if the copper tubes length is reduced.
4. Position the valve as displayed in Figure 2-2 and ensure the arrow mark aligns with the direction
of fluid flow. The blue arrows show which way fluid is supposed to flow through the valve. Also
ensure that the MSEV series valve is installed in an upwards orientation or at any angle less than
90° in either direction (represented by the curved green arrows).

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
The MSEV series valve cannot be installed in a downwards orientation (shown in
curved red arrows). It will not function as intended if installed in this way.
Figure 2-2: MSEV series valve installation orientation
5. Wrap the valve body with a wet cloth before brazing.
6. Connect the MSEV series valve to the inlet of the evaporator by brazing. Allow the valve to air-
cool after brazing.
While brazing, direct heat away from the valve body. Ensure that the temperature
of the valve body does not exceed 221°F (105°C).
7. It is mandatory to install a brand-new filter drier at the inlet of the MSEV series valve as indicated
in Figure 2-1. It can be installed at about 6” away from the valve. The MSEV series valve must be
protected against contaminants to ensure its optimal operation.
DMQ highly recommends using a filter drier with a 20 micron filtration rating.
8. The MSEV series valve installation process is now complete.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
2.2 Installing the USHX
To install the USHX, complete the following steps:
1. Pump down and recover any residual refrigerant from the system. This may have already been
done if a MSEV series valve was installed before this step.
2. Obtain any ¼” access fitting that is compatible with the system. In this section, a ¼” access fitting
with a 3/16” OD extended tube is used as an example to demonstrate the installation process.
3. See Figure 2-3 and Figure 2-4 below for the proper orientation of the USHX. When installing the
device on a horizontal copper line as shown in Figure 2-3, the USHX can only be installed up to a
45° angle from the vertical axis in either direction (represented by the curved green arrows).
When installing the device on a vertical copper line as shown in Figure 2-4, the USHX cannot be
installed at a downward angle (represented by the red arrow).
Figure 2-3: USHX installation
orientation on a horizontal copper line
Figure 2-4: USHX installation
orientation on a vertical copper line
4. Drill a hole into the copper line that extended tubes may fit in to. The location of this hole should
be about 6” away from the outlet of the evaporator.
Care must be taken to not introduce copper shavings into the copper line while the
hole is being drilled.
5. Remove the valve core of the access fitting before brazing.
6. Braze the access fitting to the copper line and allow it to air-cool after brazing.
7. Place the valve core back onto the access fitting and tighten the connection. This step completes
the installation of the ¼” access fitting. The final result should look similar to what is shown below
in Figure 2-5.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
Figure 2-5: Brazed access fitting
8. Mount the USHX onto the access fitting. First, turn the USHX clockwise by hand until some
resistance is observed. Then, use a torque wrench to tighten the USHX to 70 in-lb as shown in
Figure 2-6.
Figure 2-6 USHX Installation with Torque Wrench (70 in-lb)
When torque wrench not available use 7/16” and 9/16” wrenches to tighten the
USHX as shown in Figure 2-7. Using two wrenches will ensure that the brazed joint is
not damaged during tightening.
Do NOT turn the power source ON during the installation of the wiring harness.
Figure 2-7 Installed USHX with attached 10-pin wiring harness
9. Attach the wiring harness (10-pin connector) to the USHX as shown in Figure 2-7.
If the USHX is located in a wet or potentially wet environment, apply silicone grease
inside the 10-pin connector of the wiring harness.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
10.Install the thermistor at the outlet of the evaporator and close to the access fitting using a zip tie,
as shown below in Figure 2-8.The thermistor should be located at either the 10 o’clock or 2
o’clock position only.
Figure 2-8 Thermistor installation at evaporator outlet
Ensure that the thermistor wire is not tied down to the tubing. The zip tie should
only be tied around the thermistor body.
Apply thermal grease between the thermistor and the copper line to obtain the
most accurate temperature readings.
11.Wrap the thermistor with the insulation material and secure the insulation in place using a zip
tie. The final result should be similar to what is shown below in Figure 2-9 .
Figure 2-9 Insulation secured to the thermistor
12.Check for leaks at all the braze joints after brazing.
13.Pull a vacuum on the system until 250 microns is reached.
14.Restore refrigerant to the system.
15.Perform another check for leaks at all braze joints.
16.Refer to Section 3 (Electrical Wiring) to complete the electrical wiring of the system.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
17.Refer to USHX Software User Interface Manual to set up communications between the USHX and
the computer.
18.Supply power to the USHX with a power supply and power it on.
19.Ensure that the settings in the GUI meet the system requirements (i.e. double check the
Refrigerant, Target Superheat, Device Mode, and other settings).
20.Power on the HVAC/R system and the MSEV series valve and USHX will automatically begin
functioning.
21.Observe the superheat temperature values in the GUI Status tab to ensure that the system is
performing nominally. Adjust the system settings through the GUI if necessary.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
3Electrical Wiring
After the mechanical installation of the MSEV series valve(s) and/or USHX(s) into the system, complete
the electrical wiring of the system by completing the following steps. Refer directly Section 3.2 to if more
than one unit was installed.
3.1 Single USHC and MSEV Series Valve or Single USHS
Do NOT turn the power source ON until all electrical wiring setup is complete.
1. Check the voltage type (either 12V or 24V) of the MSEV series valve. It can be found on the MSEV
series valve model number label. The power source required will be based on the MSEV series
valve voltage type.
Ensure that the power source voltage matches the MSEV series voltage type. If a 12V
MSEV series valve is powered by a 24V power source, the valve will fail due to an
over-voltage. If a 24V MSEV series valve is powered by a 12V power source, the valve
will not fully open due to an under-voltage.
2. Obtain a Class 2 24 VAC transformer with a capacity of 40 to 100 VA and an output of 24 VAC at a
frequency of 60 Hz. Alternatively, a 120 VAC to 12 VDC or 120 VAC to 24 VDC Class 2 step-down
power supply with a 40 to 100 W power rating may be used. The schematics of the power sources
are shown below in Figure 3-1.
For the user’s own safety, only Class 2 power sources should be used to power the
MSEV series valve and USHX devices.
Figure 3-1 Class 2 DC and AC power sources
3. Double check the power source output voltage (AC transformer secondary or DC power supply
output).

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
The reading should be at or near 12VDC, 24VDC, or 24VAC depending on the MSEV
series valve and power source. When supplying 24V, the voltage must be within the
range of 20.4V to 27.6V. When supplying 12V, the voltage must be within the range
of 10.2V to 13.8V.
4. Once the power source output voltage has been identified and checked to be accurate, ensure
that the power supply is off before continuing with the steps below.
5. The power input wires (18 AWG red/black wires) on the wiring harness should be connected to
the power source as shown below in Figure 3-2.
The USHX power input wires are non-polar, so the wire ordering and colors are not
significant for the purposes of this step in the procedure. All connectors used between
the USHX, power source, and a MSEV series valve should be UL-approved.
The wiring schemes of the ‘Single USHC and MSEV series valve’ and ‘Single USHS Setup’
are the same except that the PWM output wires of the USHS for the ‘Single USHS Setup’
process should be disconnected, terminated with wire nuts, and wrapped with
electrical tape so that they do not form short circuits with each other or any other wires
or metal surfaces. As for the ‘Single USHC and MSEV series valve Setup’ process, the
PWM output wires should be connected to the MSEV series valve as shown below in
Figure 3-2.
Figure 3-2: Single USHC and MSEV series valve wiring diagram

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
6. Connect the RS485 communication wires (2-wire gray cord that contains a red and a black wire
and the green data ground wire) to the D+, D-, and SG terminals on the USB-to-RS485 converter
as shown below in Figure 3-3. For the USHX setup, the RS485 will require an adapter with built-in
electrical isolation.
Figure 3-3 USHX-to-RS485 converter connection
7. Connect the RS485 adapter box to the computer via a USB port.
8. Connect the PWM output wires (two 18 AWG white wires) to the MSEV/HC-MSEV/VHC-MSEV
electrical connections. These wires are non-polar.
9. The general purpose wires (20 AWG brown/purple wires) must remain unconnected, be
terminated with wire nuts, and wrapped with electrical tape so they do not form short circuits
with each other or any other wires or metal surfaces.
10. Tape any dangling wires to existing structures such as copper and water lines with at least 4-5
sections of electrical tape each. Use zip ties on top of the electrical tape in a neat and organized
manner to further secure the wires.
Ensure that all cables are distanced from fans, high voltage wires (120-208 VAC), and
potential areas of water. Ensure that any bare cable leads are covered with electrical
tape and do not touch other wire leads or any metal structures.
11.The electrical wiring for Single USHC and MSEV/HC-MSEV/VHC-MSEV or Single USHS setup is now
complete.
3.2 Multiple USHCs and MSEV Series Valves or Multiple USHSs
Do NOT turn the power source ON until all electrical wiring setup is complete.
1. Check the voltage type (either 12V or 24V) of the MSEV series valves. It can be found on the MSEV
series valve model number label. The power source required will be based on the MSEV series
valve voltage type.
Ensure that the power source voltage matches the MSEV series valve voltage type. If
a 12V MSEV series valve is powered by a 24V power source, the valve will fail due to

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
an over-voltage. If a 24V MSEV series valve is powered by a 12V power source, the
valve will not fully open due to an under-voltage.
2. Obtain a Class 2 24 VAC transformer with a capacity of 40 to 100 VA and an output of 24 VAC at a
frequency of 60 Hz. Alternatively, a 120 VAC to 12 VDC or 120 VAC to 24 VDC Class 2 step-down
power supply with a 40 to 100 W power rating may be used. The schematics of the power sources
are shown below in Figure 3-4. See Table 3-1 below to determine what minimum capacity/power
rating requirements must be met with these power sources based on the number of MSEV series
valves installed.
For the user’s own safety, only Class 2 power sources should be used to power the
MSEV series valves and USHX devices.
Figure 3-4 Class 2 AC and DC power sources
Table 3-1: AC Transformer Minimum Capacity and DC Power Supply Minimum Power Rating Required
Based on Number of MSEV series valves Installed
MSEV Series
Valve
Voltage
Type
Number of MSEV
series valves per
Power Source
(Maximum 6)
AC Transformer
Minimum Capacity
Required (Volt-Amps)
DC Power Supply
Minimum Power Rating
Required (Watts)
12V or 24V
1
40 VA
40 W
2
50 VA
50 W
3
60 VA
60 W
4
70 VA
70 W
5
80 VA
80 W
6
100 VA
100 W

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
3. Install the transformer or power supply at the center of the all the USHXs.
The below wiring methodology is recommended so that the load of the controllers
on either end of the transformer will be the same.
Figure 3-5 Multiple USHCs and MSEV series valves networking diagram
The wiring schemes of the ‘Multiple USHCs and MSEV Series Valves’ setup and
‘Multiple USHSs’ setup are the same except that the PWM output wires of each
USHS for the ‘Multiple USHSs’ setup process should be disconnected, terminated
with wire nuts, and wrapped with electrical tape so that they do not form short
circuits with each other or any other wires or metal surfaces. As for the ‘Multiple
USHCs with Multiple MSEV Series Valves’setup process, the PWM output wires
should be connected to the valves as shown in Figure 3-5.
4. Double check the power source output voltage (AC transformer secondary or DC power supply
output).
The reading should be at or near 12VDC, 24VDC, or 24VAC depending on the MSEV
series valve and power source. When supplying 24V, the voltage must be within the
range of 20.4V to 27.6V. When supplying 12V, the voltage must be within the range
of 10.2V to 13.8V. Do NOT Earth-ground the power source output.
5. Once the power source output voltage has been identified and checked to be accurate, ensure
that the power supply is off before continuing with the steps below.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
6. Form a daisy chain with the power lines by connecting the USHX power input cables (18 AWG
red/black wires) that are closest to the transformer on either side (USHX 3 and 4), as shown in
Figure 3-5. Use 16 AWG stranded copper wire for extensions.
The USHX power input wires are non-polar, so the wire ordering and colors are not
significant for the purposes of this step in the procedure. All connectors used between
the USHX, power source, and MSEV series valve should be UL approved. If the USHC
power input wires do not reach the system transformer add 16 AWG extensions to
the cables as needed.
7. Run the power input wires from USHX 3 to USHX 2 and then from USHX 2 to USHX 1 as shown in
Figure 3-5.
8. Run the power input wires from USHX 4 to USHX 5 and then from USHX 5 to USHX 6.
9. The USB-to-RS485 adapter is used for USHX communications. Each USHX wiring harness includes
RS485 data communication wires (2-wire gray cord that contains a red and a black wire and the
green data ground wire).
10. Create a daisy chain for the RS485 BUS as shown in Figure 3-5. Connect the gray RS485
communication wire of USHX 1 to USHX 2. Use similar communication cables when extensions
are required. Do not connect the data ground wire between USHX 1 and 2. It should remain
unconnected and protected with wire nuts and wrapped with electrical tape.
11. Similarly connect USHX 2 to USHX3 and then USHX 3 to USHX 4. Repeat this pattern until USHX 6.
12. For each transformer, only one USHX data ground wire should be connected to the RS485 adapter
signal ground input. As shown above in Figure 3-5,only the data signal ground wire (green wire)
of USHX 3 is connected to the RS485 adapter signal ground input.
13. RS485 allows up to 32 nodes (or USHXs) to be connected on one channel (or daisy chain). Figure
3-6 below shows an example of three daisy chains of 12 USHXs each.
Figure 3-6 Multiple USHXs-to-RS485 hub/repeater networking

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
14. At the end of each daisy chain, install a 120 Ωtermination resistor, as shown in Figure 3-6.
15. Procure an isolated RS485 hub/repeater. If an isolated hub/repeater cannot be found, then it is
necessary to install an isolator for each channel.
The communication cable must be kept away from high-strength electric and
magnetic fields such as those emitted from USHX and MSEV series valve power wires,
110/220 VAC wires, fan motors, relay coils, etc.
The exposed metal on the ground wires of the remaining controllers should be
covered with electrical tape.
16. Connect the isolated RS hub/repeater to the isolated RS485 adapter box. Connect the box to the
computer via a USB port.
17. Connect the two PWM output wires (two 18 AWG white wires) of each USHX to the electrical
connections of corresponding MSEV series valve. These wires are non-polar.
18. Additional general purpose wires (20 AWG brown/purple wires), if they exist on the harness, must
remain unconnected, be terminated using wire nuts, and wrapped with electrical tape so that
they do not form short circuits with each other or any other wires or metal surfaces.
19. Tape any dangling wires to existing structures such as copper and water lines with at least 4-5
sections of electrical tape each. Use zip ties on top of the electrical tape in a neat and organized
manner to further secure the wires.
Ensure that all cables are distanced from fans, high voltage wires (120-208 VAC), and
potential areas of water. Ensure that any bare cable leads are covered with electrical
tape and do not touch other wire leads or any metal structures.
20.The electrical wiring for Multiple USHCs and MSEV series valves or Multiple USHSs is now
complete.
21. Refer back to Section 2.2 (Installing the USHX), Step 17 and complete the remaining steps to
finalize the hardware installation process.

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MSEV Series and USHX Hardware Installation Manual Rev 1.7
4 Troubleshooting
The following section describes troubleshooting procedures for the USHX and MSEV series valve. If
the system is running abnormally, first check the wiring for broken or shorted connections. Repair broken
wires and remove short circuits between touching wires or between wires and any metal surfaces. If
there are no wiring problems, then use the following table to further diagnose the problem (assuming
everything else in the system such as the compressor, evaporator, filter drier, etc. is working properly).
Problem
Possible Cause
Action
High Superheat:
This may indicate
that the MSEV
series valve is not
fully opening.
Common symptoms
include compressor
short cycling.
Inadequate Power to
the Valve
Check the power source voltage. The voltage leaving the
transformer and entering the USHX should be close to the
intended supply voltage (24V or 12V). If the transformer
voltage is too low, there is a problem with the transformer or
its wiring. If the voltage entering the USHX is low and the
transformer voltage is normal, there is a problem with the
terminal connections or interconnecting wiring to the USHX.
Temperature Sensor
Incorrectly Mounted
Check the mounting of the USHC temperature sensor. The
sensor should be firmly mounted to the outlet of the
evaporator at a 10 o’clock or 2 o’clock position. Check that the
temperature sensor is wrapped with insulated tape.
Over Voltage to the
MSEV Series Valve
Check the resistance across the valve terminals. Remove both
power connections from the MSEV series valve and measure its
resistance with a multimeter. The resistance reading should be
between 26-34Ω for a 24V valve and between 6-13Ωfor a 12V
valve. If the resistance is significantly out of this range (or zero),
the MSEV series valve is damaged and should be replaced.
MSEV Series Valve
Slow to Open
Check that the USHX Gain settings meet the system
requirements. (Also applicable if the MSEV series valve opens
too quickly.)
Connect and disconnect the power to the valve several times
to manually actuate the valve.
Low Superheat:
This may indicate
that the MSEV
series valve is
staying open.
Common
symptoms include
compressor
frosting.
MSEV Series Valve
Slow to Close
Check that the USHX Gain settings meet the system
requirements. (Also applicable if the MSEV series valve closes
too quickly.)
Connect and disconnect the power to the valve several times
to manually actuate the valve.
Temperature Sensor
Incorrectly Mounted
Check the mounting of the USHC temperature sensor. The
sensor should be firmly mounted to the outlet of the
evaporator at a 10 o’clock or 2 o’clock position. Check that the
temperature sensor is wrapped with insulated tape.
Severely Oversized
Valve
Determine the capacity of the evaporator and check the valve
model number to confirm that the two are compatible
regarding their capacities.