Ford Repair: 1999 Ford Escort air conditioning, jumper wires, alligator clips

Question
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Followup To
Question -
Hello David!

The air conditioner isn't working on my 1999 Escort.   When I pull the plug from the compressor I have 13.75 volts on the plug.   When I plug it to the compressor, it is like the power "drops" out and no voltage "shows" on the wiring going into the plug (stripped wires and attached a meter to them).   When I unplug the connector from the compressor the 13.75 volts comes back!   When I attach wiring directly from the battery to the compressor using alligator clips the compressor operates and the system puts out cool air.   When I attach the wiring directly from the battery to the wires on the plug to the compressor the compressor operates and the system puts our cool air.   Would appreciate any ideas???
Answer -
Well if the compressor operates and the A/C produces cold air when power is applied with jumper wires, the mechanical part of the system is fine.  I would guess that the pressure switch is bad.  Look in the A/C line for a switch about the size of a golf ball with a two wire connector pluged into it.  Disconnect the connector and jump the wires, if the system powers up and operates normally, you've found the bad part.

I hope this helped,
Dave

Hello again David!

I failed to tell you we bypassed what I assumed was a high (high pressure side) and low pressure switch (low pressure side)in the system.   Low pressure had a two wire connector and high pressure had a four wire connector.   In each instance we ran the compressor from the powered up side of the connector to insure the integrity of the circuit.  We also used jumpers to "make" the circuit at each connector, I know this worked because the electric fan would start but the compressor would not start.   What ever the problem is, it is in the positive lead because we also tried each leg of the circuit separately.   My question is there any relays anywhere on the car for the air conditioning circuit???   I have not started at the switch and traced the circuit yet, but wonder if there is anything in the circuit I have not found, am not aware of or missed???   The only things I have found is the 15 amp fuse and the pressure switches!

Answer
Well the two wire switch is the "A/C Cycling Switch" and the four wire switch is the "A/C Pressure Cut-Off Switch".  The A/C Pressure Cut-Off Switch has two wires that open the circuit and turn off the compressor when the high-pressure side reaches 420 psi and re-close when the pressure drops to 250 psi.  The other two wires in the switch and for the high-speed fan control, they close 325 psi and re-open at 275 psi.  Be sure to test the correct two wires in that switch.  My service manual indicates that this system has a Constant Control Relay Module (CCRM) which takes inputs from the Powertrain Control Module (PCM).  The CCRM can't be serviced and must be replaced when bad, so be sure to test all wiring and both inexpencive switches before replacing.

I hope the helps,
Dave