98 Volvo S70 GLT A/C Compressor fault. Replaced AC switch 30767231, 8628563 Topic is solved

davidmk31 · Post by **davidmk31** » 10 Apr 2014, 17:06

This is my first time working on my car's A/C. Just got my check engine light to turn off when I noticed my AC wasn't blowing cold air at all. The green light comes on on the module but the compressor doesn't turn on. Last time I used it was last summer and it worked fine.

I have tried several diagnostic tests that I found searching through old threads on here, and now I need to figure out where to go from here. Here's what I've done and figured out so far:

- I was able to jump start the compressor by using a paper clip to bypass the relay in the main fuse box. The compressor clutch engaged. I had a can of R-134a plugged in at this time, and could see the PSI drop significantly as the compressor turned on, so I filled it up with the compressor on to about 45 PSI. I could feel cold air blowing in the cabin at this time.

- After I did this, I thought maybe the pressure was just low and that's why it wasn't engaging. So plugged my relay back in and started up my AC again, but again, the compressor would not engage.

- I unplugged the low pressure switch next to the firewall and used a multimeter on the switch and it read at about 12V.

- I tried jumping the low pressure switch using the paperclip to connect the contacts, but my compressor clutch did not start up.

I read a common problems include the thermal switch and the clutch "gap" problem. I believe I've ruled both these out since my clutch engaged when I bypassed the relay.

Any tips on what my next steps should be, and what the culprit could be?

Post by **Ozark Lee** » 10 Apr 2014, 17:40

It sounds like a bad relay based on what you have done. The battery voltage reading at the low pressure switch may be fooling you if there is significant resistance on the relay contacts.

...Lee

davidmk31 · Post by **davidmk31** » 10 Apr 2014, 19:20

Ozark Lee wrote:It sounds like a bad relay based on what you have done. The battery voltage reading at the low pressure switch may be fooling you if there is significant resistance on the relay contacts.

...Lee

I was wondering if that might be the case but I just don't know how to test it to see if its bad. I tried watching some instructional videos but it seems like a lot of trouble and was over my head..

I think I'm just gonna get the part though since it'll only bring me back $20 or so and hopefully that'll work. crossing my fingers..

Post by **abscate** » 11 Apr 2014, 04:38

The clutch gap issue will cause intermitant clutch operation which will make troubleshooting tough.

The pressure gauge on can readings are meaningless, check the threads on how to determine AC charge. If you are losing Freon, it's both bad for the environment and your pocketbook...like 1000s bad.

Electrically, it does look like your relay is bad.

davidmk31 · Post by **davidmk31** » 11 Apr 2014, 12:06

Ozark Lee wrote:It sounds like a bad relay based on what you have done. The battery voltage reading at the low pressure switch may be fooling you if there is significant resistance on the relay contacts.

...Lee

Alright so I picked up a new relay from the local dealer and the compressor is still not coming on. I did some more electrical testing as follows:

- I tested the low pressure switch for continuity and it was good
- I tested the voltage going into the low pressure switch and it was about 12V
- I tested the high pressure switch for continuity and it was good
- I tested the voltage going into the high pressure switch. There were three contacts and I wasn't sure which to touch, so I touched multiple variations and there were two variations that just over 5V each. Is this correct? The picture shows what I believe is the high pressure switch, just for confirmation..

So based off this, it seems that there are no problems at the low and high pressure switches (as long as my high pressure test was okay). Which leads me to believe it may be a computer problem. Does the circuit have to pass through a computer control system to provide ground for the relay? If so, where would I access this?

Post by **cn90** » 11 Apr 2014, 12:53

Ebay and junk yard has the AC relay for cheap.
Best is to find someone local and swap relay (label them first to avoid confusion).

Post by **cn90** » 11 Apr 2014, 12:56

Also,

Local auto parts store may have it.
I may be wrong but Omron 21911 should do it.

davidmk31 · Post by **davidmk31** » 11 Apr 2014, 13:33

cn90 wrote:Also,

Local auto parts store may have it.
I may be wrong but Omron 21911 should do it.

Thanks but I already tried a new relay and it didn't work (see post above). I am beginning to think the problem is my ECM. Because the voltage going to the low and high pressure switches is correct...and there is continuity on the actual switches which I believe means they are actually working correctly and the amount of pressure in there right now is okay.

Any thoughts from anyone? If I did find an ECM, does it need to be programmed?

Post by **Ozark Lee** » 11 Apr 2014, 20:34

The A/C relay is controlled by pin 40 on the ECU/ECM going to ground. From the A/C relay it is a direct path to the compressor which you have determined works. The ECU is schematically a black box and I don't have an easy way to figure out which inputs need to be satisfied for the A/C compressor circuit to engage. It would be highly unusual for the ECU to otherwise work fine but not turn on the compressor unless it isn't satisfied with one of its inputs.

The inputs to the ECU are control from the ECC, the low pressure sensor switch, and the high pressure sensor switch. The high pressure sensor wires all lead to or from the ECU so the absence of actual battery voltage isn't a surprise but I don't know what is normally opened and normally closed on the high pressure switch. I have one floating around in my garage and if I can find it (which is a big if) I will ohm it out to see which terminal pair is normally closed.

There is no special programming required for swapping a like ECU with another one in a '98 so if you have one readily available it can just be swapped. I would suspect the high pressure switch long before I would the ECU since the high pressure switch is actually fairly fragile and highly exposed.

...Lee

rbd42 · Post by **rbd42** » 24 Jul 2014, 14:44

davidmk31 wrote: Thanks but I already tried a new relay and it didn't work (see post above). I am beginning to think the problem is my ECM. Because the voltage going to the low and high pressure switches is correct...and there is continuity on the actual switches which I believe means they are actually working correctly and the amount of pressure in there right now is okay.

Any thoughts from anyone? If I did find an ECM, does it need to be programmed?

David, Having same problem on my V70XC. Did you find a solution/get the A/c working? Please tell!
Andy