AC Diode location ??

[EllowViper]

I have run into a brick wall trying to diagnose my AC problems in my 01 GTS. Just came from the shop where they did a system vacumum, leak test, recharge. Everything checks out fine. Basically I cannot get my AC compressor to come on. Checked all the pressure switches, relays, bypassed the dual pressure switch and relay all we could and still cannot get the AC compressor on. Used an ohm meter on the relay sockets and all the readings were good. Even put a new compressor on with a new clutch pack... THe service manual indicates a diode in the wiring between the fuze/relay distribution panel and the AC compressor. Not visible to the eye and must be emedded within the loom in some fashion. Anyone familiar with this and could this be the issue?? My next step is to physically check the continuity btwn the AC compressor plug and the relay via the PITA plug on top of the compressor (yes I have to remove the PS pump et al again to get at it). I know, should have done that first before I put the new compressor on, but I "assumed" a bad AC clutch pack vice a busted wire in the loom. Its not like I was messing with anything in the wiring harness that would have/could have suddenly broken the wiring to the AC compressor. Its just too hot in FLorida not to have AC. Not "cool" with the ladies either... Atleast during all this I verified the the condensor and system doesn't leak.

 

[Sweet Ride]

I have run into a brick wall trying to diagnose my AC problems in my 01 GTS. Just came from the shop where they did a system vacumum, leak test, recharge. Everything checks out fine. Basically I cannot get my AC compressor to come on. Checked all the pressure switches, relays, bypassed the dual pressure switch and relay all we could and still cannot get the AC compressor on. Used an ohm meter on the relay sockets and all the readings were good. Even put a new compressor on with a new clutch pack... THe service manual indicates a diode in the wiring between the fuze/relay distribution panel and the AC compressor. Not visible to the eye and must be emedded within the loom in some fashion. Anyone familiar with this and could this be the issue?? My next step is to physically check the continuity btwn the AC compressor plug and the relay via the PITA plug on top of the compressor (yes I have to remove the PS pump et al again to get at it). I know, should have done that first before I put the new compressor on, but I "assumed" a bad AC clutch pack vice a busted wire in the loom. Its not like I was messing with anything in the wiring harness that would have/could have suddenly broken the wiring to the AC compressor. Its just too hot in FLorida not to have AC. Not "cool" with the ladies either... Atleast during all this I verified the the condensor and system doesn't leak.

Have you checked the switch panel at all?

How about the thermostatic switch?

PCM connections?

According to my manual, the diode you are questioning is located in/around the electrical connector at the compressor/clutch.

Does the heater and/or blower motor work?

 

[EllowViper]

All blowers work. Engine fan comes on when I activate the AC. Bypassed thermo switch, etcetera. Just down to the link between the fuse/relay box and the actual AC compressor. I guess I could install my spare PCM if that could in some way be the issue. I know the PCM takes into account throttle position, MAP, thermo switch temp, dual pressure switch output and then grounds the relay circuit to activate the AC compressor. If the PCM was bad, me things the engine fans would not come on either, but that could be a separate PCM-activated ground circuit. PCM swap is pretty easy so I might try that this weekend. Just for giggles...

 

[Tiago]

need to confirm the AC request signal from inside to the PCM works. The AC request signal from the PCM to the relays work, and the power from the relay back to the compressor works. The diode should be close to where the plug for the compressor is. It is embedded in the wiring loom.

 

[EllowViper]

Thanks Tiago!! I bypassed the relay running a jumper across the 12v relay pins and nothing...so pushing 12v (13.5 actually) straight across the relay didn't work. At thing point I'm trying to remove all variables involved in the process short of running a wire directly to the AC compressor...but I might be at that point now. I'll check continuity from the AC compressor plug back to the relay out. But with the diode in there, not sure what the reading should/will be. SO what is the purpose of the diode in this equation anyways?? I also read that a good ODB-II diagnostic reader (like the dealer has) can answer the PCM-specific signals. I don't have a ODB-II reader that gets into that level of system signal monitoring.

 

[BOTTLEFED]

Eric,
a diode is like a checkvalve, not a resistor

I haven't looked at the wiring diagram, but I'm assuming it is there is keep the power from back-feeding into the PCM when not grounded

sometimes when they go bad they just close up the circuit and it reads like an open
a good multimeter will have a diode tester (pretty much reads ohms)

I could also see a wire in that harness getting cut or smashed as the loom runs by the frame and hood hinge

 

[AZTVR]

Eric,
a diode is like a checkvalve, not a resistor
sometimes when they go bad they just close up the circuit and it reads like an open
a good multimeter will have a diode tester (pretty much reads ohms)

You can get a good idea of whether it is bad just from meauring resistance both ways
Meter check of a diode : DIODES AND RECTIFIERS

 

[Jack B]

You can get a good idea of whether it is bad just from meauring resistance both ways
Meter check of a diode : DIODES AND RECTIFIERS

If you run 12V to the compressor side connector will the clutch pull in? It can be done, I had the same issue, but, it was the clutch. I checked my new compressor on the bench to make sure it pulled in - pulling that compressor is not fun.

A separate issue, the O2 circuit ground is picked up at the compressor, make sure you reattach it.

 

[EllowViper]

Thanks Jack. Good points and running a wire is my next diagnostic step. If that works, I'll have a great used AC compressor w/clutch for sale since I'll be leaving the new $450.00 one in place!! Looks like I'm having an AC diagnostics immersion session...priceless...so to speak. Oh well, one can never have too many Viper parts laying around...