posted by
someone claiming to be Robo Lobo
on
Fri Nov 9 13:32 CST 2001 [ RELATED]
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Has anyone on the board ever replaced their A/C (compressor) low-pressure switch, also known as the pressostat? I think I know where it is (passenger side near the firewall), but I want to know how easy it is for the not-too-experienced person like myself to replace, what tools I need, etc. etc. All advice is greatly appreciated.
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posted by
someone claiming to be Jake
on
Fri Nov 9 15:46 CST 2001 [ RELATED]
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My first question is why do you want to replace it as either switch rarely goes bad?
The low pressure switch is the one near the firewall and they simply unscrew, no freon will escape. I've seen a few of those fail.
The high temp switch is located on the compressor, very rarely a problem.
The high pressure switch is located just behind the right headlamp, doesn't fail as often as the low pressure switch (which isn't a common problem at all). Also just unscrews w/o freon loss btw.
The main cause of most 850 AC problems is a system low on freon and by now, most here know why too.
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posted by
someone claiming to be Robo Lobo
on
Fri Nov 9 17:26 CST 2001 [ RELATED]
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I am absolutely determined to stop my compressor from doing it's little on-off routine every time I turn on the a/c- it's driving me crazy, and my mechanic says I am not low on refrigerant. I have had the evap and compressor replaced over the last 16 months, I have installed the pollen filter, yet I still hear that ongoing tick-tock sound from the relay behind the glovebox. It's like Poe's Tell-Tale Heart.
I signed up through Alldata to get all the detailed TSBs and other technical info on my car, and there is a specific diagnosis path for my problem that points to the low-pressure switch (pressostat).
If you have any other ideas I would love to hear them, as I have asked this question on the board more than a few times: if you are NOT low on refrigerant, and yet your compressor is rapidly cycling on and off, what is the problem? The low pressure switch has been suggested, as has the high pressure switch, the orifice tube too as I remember. But no one here seems to know for sure based on their own personal experience. If you have the answer, Jake, tell me and I'll kiss the ground at your feet :-)
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posted by
someone claiming to be Jake
on
Sat Nov 10 02:50 CST 2001 [ RELATED]
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What you're then describing may be perfectly normal as it's designed to cycle on/off depending on AC system pressures. It will do that more at times than others due to outdoor temp, interior temp setting, etc.
I'd first get a second opinion as to its freon charge and the ONLY way to do that is by having the system recovered with a freon charging machine that recovers and weighs the total freon charge. By doing that, the tech knows exactly how much freon was in the system. If it's less than 1.65lbs, it's low and needs to be topped off (it's leaked from somewhere STILL or wasn't fully charged before).
Now, despite any stories you might have read, if the charge is correct, the AC blows cold at max cold settings then it's functioning correctly as designed. Throwing parts at it will only cost you more money and solve nothing.
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posted by
someone claiming to be Robo Lobo
on
Sat Nov 10 04:20 CST 2001 [ RELATED]
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Maybe I did not describe the symptoms well enough, Jake. The compressor begins cycling on and off *rapidly*, with 5-10 second intervals, pretty much immediately after I turn the a/c on. I simply can't believe that this is normal in a car that has a full charge of refrigerant.
The reason I was asking about the replacement of the low pressure switch is that it's a relatively cheap part ($36 through volvoparts.com) and it has been mentioned as a possible source of the problem.
But that being said, I absolutely agree with you about weighing the charge. My plan is to do that before my VIP warranty runs out in about 6 months, and see if the evap has gone bad again. And I'll do that even if I do replace the low pressure switch and even if my tick-tock sound has gone away.
Thanks for the advice, Jake. If you have any more ideas please let me know.
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posted by
someone claiming to be Jake
on
Sun Nov 11 06:11 CST 2001 [ RELATED]
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Yep, another idea. Bypass the low pressure switch temporarilly (only, don't leave it bypassed). By that, what you need to do is simply take a piece of wire (any wire) and make a jumper, connecting the two low pressure switch wire terminals together (unplugged) and try your AC again.
If it then does the same exact thing, cycling on/off quickly, you'll know that it's NOT the low pressure switch or being low on freon.
The high pressure switch has 3 terminals and I wouldn't advise trying to jump either of them, not likely the problem. I also wouldn't do anything with the compressor high temp sensor.
It could be an AC relay problem but I'm guessing here.
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posted by
someone claiming to be Robo Lobo
on
Sun Nov 11 14:56 CST 2001 [ RELATED]
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Hey Jake, thanks for all the good advice. I think you are right that it may not be the low pressure switch, and that it *might* be the a/c relay. At this point who knows. That being said, do I need to remove the glovebox to access that relay, or can I go around or underneath is somehow? Anyone's advice on glovebox removal is greatly appreciated. I know there have been a lot of posts abouth how to do that without messing the glovebox now, but I haven't had to do it till now. Also, if anyone happens to know the p/n of that relay I would appreciate that too.
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posted by
someone claiming to be Jake
on
Sun Nov 11 23:42 CST 2001 [ RELATED]
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I don't know that relays PN but a good dealer parts guy should be able to get you the correct part by description.
You may not need to remove the glove box but you would otherwise need to remove the knee bolster. It's easier to remove the glove box, the trick is to use a sharp tool like a test light to press on the plastic hinge type piece tabs, then they just pull upwards.
You can also try temporarily bypassing the AC relay by jumping two connectors, #30 and #87 (relay removed). To indentify those terminals, remove the relay and look at the diagram on the side of the relay itself. If you're not sure which relay is the AC relay, remove suspected relay with the engine running, compressor on and you'll notice it click off/on when re-installed.
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posted by
someone claiming to be Robo Lobo
on
Mon Nov 12 13:57 CST 2001 [ RELATED]
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Thanks again for the info, Jake. Oddly, I spoke to Dan at volvoparts.com today and he could not find the relay, or any relays for that matter, behind the glovebox. At least according to his records. So I'll probably wind up taking the glovebox off and poking around myself, trial-and-error style till I find the relay. I am hoping it's there, I've heard it's there, I guess I'll find out this week :-)
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