Heatcraft Refrigeration Products H-IM-79E User Manual

To check if the expansion valve is closing properly: 

 

Install a pressure gauge-set to suction line at  

 

the condensing unit. With the system running,  

 

close the valve on the liquid line, at the con 

 

densing unit. The system should pumpdown  

 

and shut off on the Low Pressure switch (LPS).  

 

If the system does not pumpdown and trip on  

 

the LPS then the compressor valves are weak  

 

and needs to be changed.

 

After the system pumps-down and trip on the  

 

LPS, put the system in the service mode. This  

 

will cause the Expansion valve to close. Open  

 

the valve on the liquid line, at the condensing  

 

unit. The suction pressure reading on the gauge  

 

set should not increase. If the suction pressure  

 

increases then the expansion valve is leaking  

 

and should be changed.

If the expansion valve is suspected of not functioning 
properly the motor windings resistance should be 
measured. This is a bipolar motor with two windings. 
Measure the resistance at the pins, on top of the valve, 
between locations A and B  
or C and D.  

Expansion Valve

Motor Winding

Pins

The Expansion valve position can be monitored from 
the LED display pressing the “

MONITOR” button and 

scrolling to 

ESP. This will indicate the number of steps 

the valve is open.

This can also be checked by using the EXV test pins on 
the board. This is indicated by a 0 to 5 Volts DC signal. 
At 0 Volt the valve is closed and at 5 Volts the valve is 
fully open. At values between 0 and 5 Volt, the valve will 
be opened proportionately.

Use the “

MONITOR” button to display “SCP”” 

Evaporator Suction Pressure. Record the pressure 
displayed. Start the system and observe the pressure 
displayed. If the pressure does not increase, the 
expansion valve could be defective. 

If the system is running, use the “

MONITOR” button to 

display “

SCP” Evaporator Suction Pressure. Record the 

pressure displayed. While the system is running, press 
the “

FORCE SERVICE” button. Observe the pressure 

while the system is pumping down. The pressure should 
decrease. If it does not, this indicates a defective valve.

   

A•   •C

                

   •           •

   B         D

(Note that the pins are not labeled A, B, C, D. This 
labeling is just for reference. Also, two of the pins, at 
location B and location D, have a wider spacing between 
them than between location A and C) 

For valve size 29320003 and 2930004, the resistance 
measured between pin locations A and B or C and D 
should be approximately 336 Ohms when valve is at 
75ºF.

For valve size 2930007, 29320008, 29320013 and 
29320014, the resistance measured between pin 
locations A and B or C and D should be approximately 
116 Ohms when the valve is at 75ºF.

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