tidewaterva

Trying to get my AC working for the summer on my 98 Cherokee. It has always worked well in the past needing nothing other than an occasional shot of 134. I found that the compressor clutch is not pulling in. I have checked fuses 11 and 25 in the fuse panel and also the compressor fuse in the PDC, all good. When I jumper the NO and C terminals for the compressor power relay, the clutch pulls in and the system cools fine. There is only 3.14 V at the compressor relay coil terminals in the PDC with the engine running and the controls set for cooling. I redid the battery ground connection to the inner fender- no improvement. I also tried jumpering the low pressure and high pressure pins in the connectors, and the only result is that the engine speeds up slightly. I suspect that there could be a problem with the ground side of the relay coil circuit coming from the PDC, but don't have a factory manual or wiring diagram. Also I have noticed that the electric engine cooling fan is not coming on at all. Any suggestions as to what items I should check would be appreciated.

tidewaterva

Follow up on this problem- I ordered a manual from Pacific Manuals. From the wiring diagrams and pinouts there, it appears that pin C1 on connector C3 at the PCM carries the ground signal to the AC clutch relay in the PDC. I tried cleaning the PCM pins and connectors with CRC electronic cleaner. It did not make any difference. I put a paper clip in the C3 PCM connector, and one in the relay coil socket (85) for the ground connection. There was no continuity. Would it be okay to try feeding electrical ground to a paper clip in the C1 hole in PCM connector C3? I would do this with the engine off but the ignition key on to see if the clutch pulls in. If it pulls in, it would appear that I need to replace the PCM. If it doesn't pull in, it would appear that the C1 wire is broken somewhere between the connector and the AC clutch relay. Any suggestions or advice would still be appreciated.

moparado

Don't know if i can be of some help, all i have is a generic Haynes schematic and not even for your year, up to '96 (don't laugh).
By any chance can you post the real schematic?

Have you tried replacing or swapping the clutch relay?
The AC low pressure switch via a PCM input pin is heavily factored into all this.

How did you measure that 3.14 volt reading?
Across the relay coil pins?
With relay in or out?

It could either be;
across the PCM wire to the (-) of the relay,
the AC low psi switch,
the PCM output driver,
corroded PCM/relay contacts,
or B+ end of the relay coil toward the AC selector/ignition switch.

You'll need a good reliable digital voltmeter for this.
Be careful when measuring voltages.

First make sure you've got good B+ battery voltage at the relay coil (+) pin.

To test the PCM output driver; AC on, relay installed, PCM connector plugged in.
Measure the voltage across the PCM relay coil output pin to ground.
It should be close to 0 volts.
Might have to scrape some insulation off that PCM wire.

If its near B+ voltage, then maybe the PCM is not getting a AC low psi switch signal; bad switch, wiring or low freon?
According to the Haynes schematic, the AC low psi PCM input pin needs to be at B+ voltage in order for the PCM to enable the relay coil output pin to ground.

If its near 0 volts, the PCM is doing its job.
Then i'd start looking at wiring to the relay, spread or corroded contacts or a shorted relay to B+.

I had heater blower issues couple years ago. Changed the blower relay then took the old one apart. It was corroded to hell inside; contacts and coil.

tidewaterva

Moparado,


Thanks for the good suggestions. I replaced the AC clutch relay- no change in anything. Testing the low pressure switch, it has 13.34 volts coming to the switch on 1 of the connector pins. It measures 1 ohm of resistance across the switch pins, so it seems to be fine. Likewise the high pressure switch has 13.34 volts on one of the connector pins. It does not make any difference if I jumper across the connector pins, or leave them open. Still no relay pull in. I checked the relay socket pins in the PDC and found that pin 3 has about 1050 ohms of resistance compared to the negative battery terminal. I believe that is the ground feed from the PCM, which may be OK. Measuring voltage at pin 5 referencing the battery ground terminal, there is no voltage. I think this is the problem. I am going to recheck fuses 9 and 27 in the PDC.

tidewaterva

I pulled the cover off the bottom of the PDC. The white wire connected to terminal 5 of the AC clutch relay only has 3.43 vdc with the key on and controls calling for AC. I have traced the wire back in the harness to where the harness takes a turn and is routed across the firewall towards the drivers side. There is still only 3.43 volts in the white wire. I am going to remove the junction block (fuse block) in the passenger side kick panel. There is 13.34 vdc coming to one side of Fuse 11. Since the engine cooling fan and AC stopped working at the same time, and both of the control ckts are fed by F11, I hope to find a loose connection on one side of F11 at the junction block.

tidewaterva

I could not remove the junction block (fuse block) due to poor access to the top mounting bolts. looks like it would require further disassembly of the right side dash and or glove compartment to get it out. Best I could do was to unseat and reseat connector C2 which is supposed to carry the 12v power to the cooling fan and AC clutch relays. Reseating the connector did not do any good. So rather than go any farther trying to remove the fuse block I connected a fuse holder with a 20A fuse to the 12vdc positive power terminal outside the PDC, and ran a 10 ga wire inside and butt spliced it to the cooling fan relay power wire and the AC clutch power wire. I checked to make sure that the relays don't pull in with the key off which they don't. The AC relay pulls in fine now with the engine running and when the controls are set for cooling. I am assuming that the cooling fan will kick in when the engine temp gets up to its setpoint. I hope that the information I have posted will help someone have this problem in the future.

freegdr

Seem others have this issue...

tidewaterva

Yes I could have that going on although this jeep has very little corrosion anywhere. If more stuff goes wrong with the fuse block in the future it would have to be replaced.