AC works when jumpered at the relay.

Post by **firestix** » 13 Jun 2012, 15:59

Ive browsed around the site and cant find anything definitive on troubleshooting this lack of AC.
So lets tell you whats going on... I'm about to move to LA and will need AC. SO i took my 98 V70R to the garage where they told me the AC compressor was seized. SO I had that replaced. The compressor works fine if we jumper at the relay. I can't however seem to get signal to the relay to make it work properly and cycle under the control of the ECM? from what I'm gathering. The mag side of the relay measures about .5 v no matter what I do on the control panel in the car. We have power to all the controls in the cabin, I even tried swapping in another cabin controller. So I guess what I'm getting at is am I really looking at a new ECM to get my AC to work? Is there something else I should be checking? Sensors that might tell the ECM not to let the compressor turn on? Is there a way to get the cabin controls to flash codes to tell me what is wrong? Or am I really gonna have to take this back to the expensive garage to get it fixed or worse yet the stealership?

Post by **MoVolvos** » 13 Jun 2012, 17:08

firestix wrote:The compressor works fine if we jumper at the relay.

Do you mean runs fine or the pressure in the system fine meaning full charge?

Blessings,
BKM
-

Post by **jimmy57** » 13 Jun 2012, 20:28

Pull the ecm out of the control module box for 5 minutes. I have seen Bosch Motronic ECM's do this several times. It likely will never do it again.
The high side pressure sensor on the line just below and in front of the control module box can keep compressor from running but if it was working fine before compressor died then it is likely OK.
Does the shop that did the work have a scan tool that can read live data from the ECM?

Post by **firestix** » 14 Jun 2012, 01:15

BKM98 S70 T5 wrote:
firestix wrote:The compressor works fine if we jumper at the relay.
Do you mean runs fine or the pressure in the system fine meaning full charge?

Blessings,
BKM
-

I mean I can hear the clutch engage and then cold air starts to blow out of the vents. So, as far as I can tell the relay is not getting the signal to turn on the compressor.

Post by **firestix** » 14 Jun 2012, 01:26

jimmy57 wrote:Pull the ecm out of the control module box for 5 minutes. I have seen Bosch Motronic ECM's do this several times. It likely will never do it again.
The high side pressure sensor on the line just below and in front of the control module box can keep compressor from running but if it was working fine before compressor died then it is likely OK.
Does the shop that did the work have a scan tool that can read live data from the ECM?

Ill try that pull the ECM thing out.
As for the pressure sensor who knows? The AC has not worked since the car became mine. Can I put a multimeter on it to tell if the sensor is the problem?
As for a scan tool, I have one(Scan guage 2) but its not Volvo specific so I don't know if it will help me out with this.

Post by **jimmy57** » 14 Jun 2012, 07:30

The a/c pressure sensor center wire is the out signal as I recall. 20 psi would be 0.3V and 400 psi is 4.2V (approximate values).
One of the other wires is ground and would 0.0-0.2V and the remaining would be the 5V supply from ECM.
If you use a straightened paper clip or much better a T pin (floral arrangements and hobby use, make FANTASTIC backprobing probes) stuck through the rubber seal around the wire you can get these readings.