2007 S40 AC compresssor not turning
 

Hey guys - so I thought I'd be diagnosing the AC on my wifes car as the compressor clutch gap being too high... and maybe it is, but at the same time I also checked the voltage at the compressor and there isn't any. I'd assume the yellow/green wire from above (when laying under the car with the splash shields off) is +12v? If so, I have no voltage on that with the AC button depressed inside the car. I had my wife cycle the AC button and I also can't really feel the compressor click at all, no change in idle at all, and I also held the AC compressor relay and don't feel that click at all.

The issue was that she would drive and have AC for the first like 1 - 2 miles of driving, then it'd go humid and gross and no AC. I checked the clutch gap and can fit a 0.5mm - 0.6mm feeler under the clutch cover between the pulley and clutch cover. But, even still, I don't measure any voltage at the 1-wire connector at the compressor. Any thoughts here guys? Checked the fuse, it seems ok. Replaced it with a spare. Same deal. I am going to order an AC relay for the hell of it... but before I start down the electrical path is there anything else I should look for?

Thanks!

there's also pressure sensor switches (hi and low) that can trip off the compressor. The low pressure is on the return between the firewall and compressor. You can try removing the connector from the sensor then jumper to see if you can get the clutch to kick in. If so, your freon may be low. The symptoms of the clutch gap problem is the clutch engages when cold (ie first few miles of a drive) then as it slips it heats up and trips the compressor off due to heat build up (a clutch that doesn't slip won't build up heat). Relays can also go wack when they warm up so that's not a bad idea to check out before taking on the clutch shims. There you should be able to jumper as well to see if you can get the clutch to kick in. Do you have any flashing REC/AC lights? if so that's the climate control computer thowing a code...

Final thought is you can trace the wires by looking at the diagrams at volvowiringdiagrams.com - not that easy to read but at you can see, there are several bits that get involved - high and low pressure sensors, temp sensors, climate control computers can be bothered by faulty blowers and resistors. Doesn't sound like they are in play given you noted it kicks in when cold then you lose AC after a few minutes. Sounds like the clutch gap issue to me. Also there was a recent post on how to access the AC clutch through the tire well. Not sure if that was for a Gen1 or Gen2 S40 but it was an excellent write up.

Thanks man very helpful

Does jumpering the pressure switches bypass them? I can try that. It could be the clutch spacing also. I tried the "zip tie under the straps" thing and couldn't get the clutch to come on. My wife is certain that the AC worked a little bit this morning (it was 68 - 70F out though).

Do you know if the wire at the AC compressor is the +12v? It was green/yellow and junctioned to a black wire coming off the compressor. It was a single pin connector. It's a Gen 2 I believe, so I had super easy access to the compressor through the wheel well with the liner out.

you don't want to bypass the switches for anything other than testing/maintenance or you'd risk your compressor. The idea of the clutch gap problem is when the gap is too large (say .8mm or more) there's not enough pressure and the clutch slips, heats up and the compressor shuts off. So when you first start up, the AC will blow cold and then when heat builds up, it trips off. There's a great recent thread with pics on how to remove the clutch - not sure if its on this board or the 850's. The idea of jumpering the low pressure sensor is that if you can get the compressor to stay on, it will take a freon fill. So you can use that trick to test (briefly) and to help get a pressure reading to make sure you don't need a charge. I have not tried to measure a clutch gap but if you can sneak in with a feeler gauge - "good" is in the .4mm (.015 inch) range, bad is over .8mm (.030 inch). Oh and the zip tie/bread bag clip thing never worked for me either...

Would it be uncommon for the AC not to engage at all with the clutch? I was idling the car around 3 - 4 PM the other day and couldn't get it to engage, even bumping it.

I was trying to look for voltage at the clutch to see if its even getting power - do you know what the connector looks like? I wouldn't jumper the pressure sensors for anything but testing. So its a true jumper in the connector that will bypass them, not a certain resistance? Thanks!

Replace broken AC low pressure switch
 

Btw, is it easy to replace the AC low pressure switch? Do I need to drain the freon or is there a presta valve under the switch that would prevent freon from leaking? I read in the forum that other Volvo models will not freon if you remove the low pressure switch. Just wondering if it is the same for a 2011 S40 T5. Thanks!

Are you having an issue like above? This model is infamous for needing a re-shimming. It took me about 10 minutes to remove the clutch face and remove one of the shims to bring the clutch gap back into spec.