AC Compressor High Pressure Switch?

kevinh · Post by **kevinh** » 05 Mar 2010, 15:58

Hello,

I'm new to the forum (although I've viewed it plenty) but a Volvo owner for 12 years (wife's wagon). Our mechanic is replacing the ac compressor and clutch. I ordered a reman unit from europartsdirect. He called this afternoon and said that the old one had a high pressure switch but the replacement didn't have one. He indicated it would be okay and could be adapted but might cause a problem if the engine got really hot (I think) and wanted to let me know before he replaced it. Anyway, does anyone know if this switch is imperative or not? The replacement was the correct one and they are trying to contact the remanufacturer (Hancock) to see why the switch is not on it. Thanks for any help on this issue.

Post by **Ozark Lee** » 05 Mar 2010, 16:28

Welcome to MVS,

On your '98 it should be pretty much the same as my 850s and there really is no high pressure switch on the compressor itself. The high pressure switch should be located on the frame rail next to the window washer fluid tank. The 850's did have a thermal cutout switch but anyone who has ever had a problem with it just bypasses it and carries on. On all of my 850s the compressors are Zexel brand but yours may differ, I think some models had Nippon Denso compressors.

...Lee

dchilders · Post by **dchilders** » 06 Mar 2010, 18:32

so Lee where is this "thermo????" located and how do you bypass....sounds like heart surgery....is it that hard of a procedure?

Post by **Ozark Lee** » 07 Mar 2010, 05:00

The thermal limit switch is just a series switch that is in-line with the positive battery voltage to the compressor clutch - it is simply a matter of removing it from the circuit and running the gray wire straight to the compressor clutch to bypass it.

...Lee

awyeth · Post by **awyeth** » 03 Aug 2010, 22:32

I am a brand new Volvo owner (1996 Volvo 850 Turbo) and not mechanically minded. I just bought this baby for $1900 and I love it except it has an all black interior, I live in Alabama and the ac doesn't work....a bad combination. Air blows but the air isn't cool. I had the freon recharged and that helped for a while...and the guy said he saw no leak. Could it be this switch thing? Am I hopelessly out of my league to try to "bypass it"? If I take it to the shop, what should I tell them to do so I can avoid buying a whole new ac system on a 1900 vehicle? Thanks for your patience with a newbie and thanks for the advice!

Post by **Ozark Lee** » 04 Aug 2010, 05:45

The reason that they saw no leak is because it is likely leaking at the evaporator which is buried deep in the dash. It is not a horribly difficult job to replace it but a shop will charge you at least $1200 to do it. It looks more difficult than it really is.

http://www.woodjoiner.com/volvo/

...Lee

Post by **Red-Arrow** » 27 Aug 2010, 05:03

What is the normal pressure for the AC system on the high or low side port?

My compressor is new but the clutch just won't engage. I'm thinking I'll get it leak tested and watch the drain for the condenser.

I really hope its the high pressure switch. How much doe these cost from a dealer? when you guys main bypass it your taking about just giving the compressor a positive wire from a source in the engine right?

Your not talking about physically cutting it out of the line and then splicing in a new section of pipe like some kind of plumber?

Post by **Ozark Lee** » 29 Aug 2010, 20:43

We don't have a high side pressure port, only a low pressure port which is just below the power steering pump. Normal pressure depends very much on the ambient temperature - the hotter it is the higher the pressure will be - but with the compressor running you should see a low pressure reading in the mid 30 PSI range. I'm not sure what that is in bar which may be a more familiar measurement for you. Without the compressor running, on a hot day, it can get up to around 120PSI (low side) on a properly charged system.

...Lee

bigwong · Post by **bigwong** » 30 Aug 2010, 11:20

one bar is one atmosphere which is 14.7 psi. 30 psi would be ~2 bar.

Post by **Red-Arrow** » 30 Aug 2010, 23:49

Ozark Lee wrote:We don't have a high side pressure port, only a low pressure port which is just below the power steering pump. Normal pressure depends very much on the ambient temperature - the hotter it is the higher the pressure will be - but with the compressor running you should see a low pressure reading in the mid 30 PSI range. I'm not sure what that is in bar which may be a more familiar measurement for you. Without the compressor running, on a hot day, it can get up to around 120PSI (low side) on a properly charged system.

...Lee

What is the physical or electrical test for the AC pressure switch?

I believe the problem is the AC high pressure switch as there are no leaks and the system is pressurized. Can anybody tell me the part number for the AC pressure switch and who would sell this for non dealership prices? I think the dealers charged around $150 for the switch alone.

Also if I replace this switch will all the freon escape under pressure? What other Volvo's or cars have the same part? if the AC switch is too expensive I may just go to the junk yard.