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A/C thermo switch question


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4 replies to this topic

#1 ndsnewleg

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Posted 30 May 2005 - 06:58 PM

My a/c cycles on and off too frequently after a few minutes of running (cold). The freon seems to be up to pressure. Checked myself w/ guage. I can hear the evap/thermo switch clicking so I found a couple u-pick salvage ones. I found the right part but it came off a car w/230K. I also got one from a 94 (140K). Looks exactly the same. Only difference I can see besides second half of part # is the one for my car (90 legacy) is rated at 0C degrees whereas the 94 is rated at 1.5C degrees. Anyone think there would be a problem if I spliced in the newer one. The 4wd evap's only interchange from 90 to 93. The 2wd's interchange from 90 to 94. Thanks

#2 Legacy777

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Posted 31 May 2005 - 07:49 AM

Are you sure it's not a charge issue, rather then the switch issue?

#3 ndsnewleg

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Posted 31 May 2005 - 12:04 PM

Hi Josh, you've helped me previously through your web site a couple of times. So, thanks again. I checked it with with one of those tire guage looking a/c slider gauges. It measured about 32 psi on the low side at about 80 degrees outside temp. Don't know if I need to be more high tech than that, ie., professionally checked at a shop. It blows very cold for 5 to 10 mins and then gradually starts to cycle on and off rapidly. I've pulled the glove box to see if I could hear the switch clicking and I do hear it. I suppose I could have pressure checked at a shop to be more certain but wasn't sure the expense was necessary. Let me know if you have info or advice to the contrary.

Thanks, Ron

#4 Zack

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Posted 31 May 2005 - 10:14 PM

I checked it with with one of those tire guage looking a/c slider gauges. It measured about 32 psi on the low side at about 80 degrees outside temp. Don't know if I need to be more high tech than that, ie., professionally checked at a shop. It blows very cold for 5 to 10 mins and then gradually starts to cycle on and off rapidly. I've pulled the glove box to see if I could hear the switch clicking and I do hear it. I suppose I could have pressure checked at a shop to be more certain but wasn't sure the expense was necessary. Let me know if you have info or advice to the contrary.


A side question (I hope this doesn't count as attempting to hijack the thread!) -- how DOES one check AC pressure? What sort of tools do you need, and at what point in the system do you take the measurements?

Thanks,
Zack
'90 Legacy wagon auto awd 158,000 miles

#5 Legacy777

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Posted 01 June 2005 - 07:57 PM

To be quite honest, without knowing the high side pressure, it's hard to say whether it's the switch or the fact the system is generating too much pressure.

My nissan pickup cycles on and off too frequently. When I checked the low side pressure, things looked ok, but the high side was too high. I'm pretty sure it's overcharged. I'm planning to just evacuate everything, clean the system out, put the specified amount of oil back in, and recharge the system.

Personally, I'd just take it to a shop that will give you an ac system diagnosis for a specified amount of money. Most shops will do that. I had mine looked over for like 30 bucks or something.

Other option is to buy the manifold gauges, which is about 100 bucks. Then, if you want to do the work yourself, you need a vacuum pump as well.




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