Brochure

Parker Hannifin Corporation
Climate & Industrial Controls Group
Cleveland, OH
Catalog CIC-2003-1/US
Thermostatic and Constant Pressure (Automatic) Expansion Valves
188
Proper Wiring of Valve and Thermistor
Thermal Electric ValvesTroubleshooting
Troubleshooting
Testing For Proper Operation
The valve and thermistor should be wired in series as
shown in the illustration below. All wiring should be
made in accordance with U.L. low voltage class 2
codes.
Some Precautions
1. Never apply more than the output of a 24 volt trans-
former to the valve circuit.
2. Don't apply 24 volts directly across the thermistor
leads. It will short out the valve and damage the
thermistor if both terminals of the electric valve are
touched with one volt-ohmmeter lead.
Initial Electrical Checkout
If the electric valve and/or thermistor are suspected to
be inoperative, check the following:
1. Are the electrical connections to the valve and ther-
mistor tight and correctly wired?
If the connections are okay, continue to step 2.
2. With the transformer disconnected, make a simple
electrical continuity check of the valve and ther-
mistor using the volt-ohmmeter.
Service Gauge Manifold Tests
If no problem is found during the volt-ohmmeter tests,
reconnect the power supply and connect a service
gauge manifold to the system. Then observe high and
low side pressures during the following tests:
1. To see if the valve is closing:
Remove voltage to the valve by disconnecting any
wire in the circuit.
With the circuit open, low side pressure should
begin to drop. Wait three or four minutes, if the
pressure does drop the valve is closing freely and
is not clogged or sticking.
2. To see if the valve is opening:
Remove the thermistor from the circuit by placing a
jumper wire across the two thermistor leads. This
will send 24 volts directly to the valve.
With 24 volts at the valve as the valve opens, low
side pressure should begin to increase. If low side
pressure does increase, the valve is opening prop-
erly and is okay. Note that this kind of testing cannot
be done with a capillary tube system.
With a thermostatic expansion valve system, the
thermal bulb has to be removed from the suction line
and heated to see if the valve is opening properly.