Getting power to the relay but nothing to the compressor

[Notnilc20]

When I jump the relay the compressor kicks on so the wiring should be fine between the relay and clutch. But I checked anyway for continuity on the wire between the relay terminal that feeds the compressor clutch and it read 1.4 ohms.

Then something has to be amiss in the area of the relay...maybe the relay itself or a loose female plug?

ok yeah, I thought about that as well, but when jumping it there is no problem to jump the power. I even tried taking the fuse block off to get to the wiring connectors but it was getting a little tricky so I stopped. However, as I said, the terminals jump no problem.
Here's another strange thing. on the relay terminal 30 and 87 is the switch and 85 and 86 is the control with the electromagnet that pulls the lever over to connect 30 and 87. If I probe the terminal 85 that connects to the pcm (terminal 55 on the pcm) without the relay in I get around 4 volts. But If I plug the relay in where I can get a test lead on that leg of the relay it now reads 12 volts.
So, I'm getting;
1) 12v to the always hot,
2) 12v to the hot with key on,
3) 12v to the control to pcm,
4) but the power is not reaching the terminal that connects to the compressor clutch. This seems like a relay issue but I've tried tested good relays and still nothing. I tried wiggling the relay while it was plugged in, in case there was a worn female terminal like you suggested but nothing. I am scheduled to take it to a shop Monday but I'd rather not because they always rake me over the coals but if I can't figure it out then I guess I need to. Do you have any other suggestions? Is there anything with the terminal 55 on the pcm
(relay control) reading 4 volts when relay is not plugged in and reading 12v when its plugged in? Thanks so much for your time thus far.

[JohnHere]

ok yeah, I thought about that as well, but when jumping it there is no problem to jump the power. I even tried taking the fuse block off to get to the wiring connectors but it was getting a little tricky so I stopped. However, as I said, the terminals jump no problem.

Who said that troubleshooting an MVAC system was easy?

Here's another strange thing. on the relay terminal 30 and 87 is the switch and 85 and 86 is the control with the electromagnet that pulls the lever over to connect 30 and 87. If I probe the terminal 85 that connects to the pcm (terminal 55 on the pcm) without the relay in I get around 4 volts. But If I plug the relay in where I can get a test lead on that leg of the relay it now reads 12 volts.

Looking at your schematic, I don't see Terminals 30, 85, 86, and 87 on the relay unless I'm missing them somehow. But I DO see Terminal 55 on the PCM.

Here's another strange thing. on the relay terminal 30 and 87 is the switch and 85 and 86 is the control with the electromagnet that pulls the lever over to connect 30 and 87. If I probe the terminal 85 that connects to the pcm (terminal 55 on the pcm) without the relay in I get around 4 volts. But If I plug the relay in where I can get a test lead on that leg of the relay it now reads 12 volts.

Looking at the schematic for the "A/C Compressor Clutch Relay," we have a 10A fused wire coming down from "Hot In Run & Start" to Terminal 2 at the relay. The same Terminal 2 connects to the top "VVVV" line inside the relay, which signifies a resistor of some unknown value; and also to the "UUUU" line just below the resistor, which signifies an inductor or coil/solenoid that generates the magnetic field that closes the relay's internal switch.

Therefore, if we have 12V coming down the wire to Terminal 2 with the relay plugged in, you should see LESS than 12V output at Terminal 1 (because of the resistor), which feeds into Terminal 55 of the PCM. The feed voltage into the PCM should probably be about 4V (the PCM is very sensitive to full battery voltage), which you measured previously at 4V without the relay plugged in. This is an impossibility because without the relay in place, Terminals 1 and 2 CANNOT be energized—unless you have a short-circuit in the wiring underneath the relay.

If you have 12V coming out at Terminal 1 of the relay, which you said you did, the relay itself could be defective (which you have ruled out) or something is energized when it shouldn't be (the short-circuit mentioned above). In addition, the PCM has now been subjected to full battery voltage of 12V, probably destroying or "frying" the sensitive electronics inside.

[Notnilc20]

ok yeah, I thought about that as well, but when jumping it there is no problem to jump the power. I even tried taking the fuse block off to get to the wiring connectors but it was getting a little tricky so I stopped. However, as I said, the terminals jump no problem.

Who said that troubleshooting an MVAC system was easy?

Here's another strange thing. on the relay terminal 30 and 87 is the switch and 85 and 86 is the control with the electromagnet that pulls the lever over to connect 30 and 87. If I probe the terminal 85 that connects to the pcm (terminal 55 on the pcm) without the relay in I get around 4 volts. But If I plug the relay in where I can get a test lead on that leg of the relay it now reads 12 volts.

Looking at your schematic, I don't see Terminals 30, 85, 86, and 87 on the relay unless I'm missing them somehow. But I DO see Terminal 55 on the PCM.

Here's another strange thing. on the relay terminal 30 and 87 is the switch and 85 and 86 is the control with the electromagnet that pulls the lever over to connect 30 and 87. If I probe the terminal 85 that connects to the pcm (terminal 55 on the pcm) without the relay in I get around 4 volts. But If I plug the relay in where I can get a test lead on that leg of the relay it now reads 12 volts.

Looking at the schematic for the "A/C Compressor Clutch Relay," we have a 10A fused wire coming down from "Hot In Run & Start" to Terminal 2 at the relay. The same Terminal 2 connects to the top "VVVV" line inside the relay, which signifies a resistor of some unknown value; and also to the "UUUU" line just below the resistor, which signifies an inductor or coil/solenoid that generates the magnetic field that closes the relay's internal switch.

Therefore, if we have 12V coming down the wire to Terminal 2 with the relay plugged in, you should see LESS than 12V output at Terminal 1 (because of the resistor), which feeds into Terminal 55 of the PCM. The feed voltage into the PCM should probably be about 4V (the PCM is very sensitive to full battery voltage), which you measured previously at 4V without the relay plugged in. This is an impossibility because without the relay in place, Terminals 1 and 2 CANNOT be energized—unless you have a short-circuit in the wiring underneath the relay.

If you have 12V coming out at Terminal 1 of the relay, which you said you did, the relay itself could be defective (which you have ruled out) or something is energized when it shouldn't be (the short-circuit mentioned above). In addition, the PCM has now been subjected to full battery voltage of 12V, probably destroying or "frying" the sensitive electronics inside.

My apologies. I was posting the reply going off memory. I went home today and rechecked and the voltage was not 4v as I incorrectly stated in fact it was 0.4 volts with the relay unplugged. Sorry about that. I don't know if 0.4 volts is relevant enough but it does read this at the relay terminal and terminal 55 on the pcm only when the relay is unplugged.

I tried posting another pic of the relay labeled but the file is too large. So with the current wire diagram from top to bottom. the numbers are
86
87
30
85

Also, to rule out the loose remale Terminals I had the relay plugged in and I took a small pin and was able to get a reading on all the relay prongs while it was plugged in and confirmed 12v on all the prongs except the prong 30 which feeds the clutch.

[JohnHere]

I don't remember anymore, but did you replace the pressure sensor on the evaporator tube? It should have a Schrader valve behind it, eliminating the need to recover the system beforehand.

[Notnilc20]

I don't remember anymore, but did you replace the pressure sensor on the evaporator tube? It should have a Schrader valve behind it, eliminating the need to recover the system beforehand.

Yes that was one of the first things I did. I finally fixed it. Well I took it to a mechanic who tested everything and he said the pcm was not grounding the relay so the pcm was bad. Since my pcm was still under warranty I recieved another one and viola! It works now. Thank you John for your insight and your time in helping me. Until next time...

[JohnHere]

Well, it took a while, but very glad you found the problem. Appreciate your following up and letting us know.