Its winter time, but

where would one start in looking for the culprit of a failed a/c?

When i bought the car, the guy just said "it doesnt work".

thanks

 

Check freon level.
Check the compressor clutch.
Check the sensors.

 

Just worked through this issue. The short story is that I had voltage to the connector just above the compressor but the clutch would not engage. If battery voltage was applied directly the clutch would engage and the A/C would work. The problem turned out to be a bad solder joint in a relay in the interior controller panel. Had to remove the lighter panel and the radio and rack to get to the controller. Once it was removed and opened, a careful look at the solder on the relay terminal revealed the defect. A bit of solder later, back in business.

If you don't have voltage to the connector at the compressor the high and low pressure switches need to be checked as either can (and should if a fault is present) prevent voltage from reaching the compressor clutch.

 

Congrats on the fix! What year/model Volvo do you have? I have a '91 740 turbo that has great A/C, sometimes. I suspect the compressor delay relay but have been unable thus far to figure out where it's hidden. Sounds like the one you found was behind the A/C control panel?

 

The AC in my 88 245 works great.... for about 5 minutes. Then it's slightly cooler than outside-lukewarm. Drives me crazy. Is there any common problems that I should check out? Could anyone point me to a good thread about 240 AC problems?

 

My problem was with a 1995 940 but am unsure it would apply to your 740 as well. My problem was with the actual heat/AC/fan control panel. There was a bad solder joint on the back of the panel. It was a known issue but took me a while to find the thread. It would have saved me much effort had I found it sooner. Unsure about the relay you are talking about. It seems feasable that it could be your problem as I've had to replace other relays for failure under load also. My overdrive relay failed in a fashion similar to your description.

I would think if I had your problem I would check for voltage at the connection nearest the compressor when it fails. ( I am assuming your compressor is not engaged anymore when you have your problem) If you don't have voltage there, see if you have voltage at the pressure switches. If voltage is present before a switch but not after it, you need to investigate further as to why the switch remains open. Is it failed or just doing it's job protecting the system. A set of gauges to verify system pressure would be necessary at this point to verify.

My problem started as an intermittent one but quickly became a total failure. I don't recall it being a time running issue so much as a work today, not tomorrow, issue.

Good luck,
Dennis