850 a/c works only in morning (not clutch, not charge)

mc510 · Post by **mc510** » 29 Jul 2007, 16:47

A/C compressor on my 1996 850 wagon (156,000 miles; auto trans; not turbo; not automatic climate control) seems like it will activate only in the morning (i.e., when temperatures are cool; around 60F/16C) ... later in the day, when the temperature is a bit warmer, the compressor will not activate at all. The blower works fine at all times, and when the compressor decides to work it seems to work fine.

I tried bypassing the low pressure switch -- no effect. Added a can of refrigerant -- no effect. Shimmed the clutch to reduce the gap from 0.8mm to 0.2mm -- no effect.

What's left?

ken goodman · Post by **ken goodman** » 29 Jul 2007, 17:11

the clutch coil is going bad electrically we have been replacing the compressors in droves for several years now. the coil is not available and a new compressor will improve cooling greatly. hope this helps

Post by **Ozark Lee** » 29 Jul 2007, 22:16

Before you punt, check the relay and the pressure switch. The next time it fails check your compressor lead and see if you have battery voltage when measured against the frame. If not, backprobe the leads at the "pressostat" and again look for battery voltage on both leads when measured to ground. If one side is hot and the other isn't, replace the pressure switch. If both sides have no voltage move to the cabin (behind the golve box) and check the A/C relay.

If you do have voltage everywhere and the compressor doesn't run it is indeed new compressor time.

...Lee

mc510 · Post by **mc510** » 29 Jul 2007, 23:26

Ozark Lee wrote:Before you punt, check the relay and the pressure switch.

Will do, Lee ... I see some references to a high-temperature cut-out switch as well ... not sure where it is or what it looks like, but is that also something to check?

Post by **Ozark Lee** » 30 Jul 2007, 09:09

I see some references to a high-temperature cut-out switch as well ... not sure where it is or what it looks like, but is that also something to check?

It is bolted on with the compressor. If you trace from the bullet connector at the compressor it goes through a "black box" before going in behind the clutch. The black box is the thermal cutout.

...Lee

mc510 · Post by **mc510** » 30 Jul 2007, 19:35

Okay, it's a comfortable 69F deg outside right now. I just started 'er up and switched on the fan and a/c ... compressor clutch does not activate. Pulled the connector off of the low pressure switch and tested for current ... no current on either connector terminal (when grounded to engine block). I guess that's good news? Something other than compressor is at fault.

When I have a little more time I'll yank the glove box and test at the a/c relay. If I'm reading the wiring diagram correctly, I could be looking at a faulty relay (that reacts to ambient temperature?), faulty ECU (which controls the relay), or a faulty sensor that the ECU is responding to. Other thoughts welcome!

Post by **Ozark Lee** » 30 Jul 2007, 20:25

Actually the ECU gets an input from the A/C circuit - it adjusts the idle mixture to compensate for the additional load - rather than an output from the ECU to activate the compressor. If your blue AC light is illuminating on the climate control panel and you have no voltage at the pressure switch I think you have narrowed it down to either the relay or the wiring to or from the relay.

Way cheaper than a compressor!

...Lee

mc510 · Post by **mc510** » 30 Jul 2007, 21:10

that IS good news! any idea where I can get a replacement relay (other than the dealer)? Doesn't appear that FCP Groton has them.

Post by **Ozark Lee** » 30 Jul 2007, 21:45

FCP can get you anything Volvo if you call and ask. They usually save a few bucks on stuff you would otherwise get at the dealer. The freight may eat the savings up though. It is a free call so its worth a shot.

...Lee

mc510 · Post by **mc510** » 03 Aug 2007, 20:02

Yep, the a/c relay was not closing ... but not because the relay was bad. The problem was the fan speed switch! If the fan is on at any speed, the fan speed switch is supposed to deliver +12v to the a/c relay (terminal 86). But it was only delivering 1.5v, which seems to be not enough to activate the relay. I removed the fan speed switch, disassembled and cleaned contacts, put it back in and all is good. (While I was at it I also removed, disassembled, and cleaned the recirc and a/c switches ... this was A Bad Idea as it wasn't really needed and was real tricky to take apart and reassemble). I still have no idea why the a/c had been working on cool mornings but not warm afternoons.