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  1. #1
    Jr. Mechanic
    Join Date
    Apr 2011
    Location
    Wylie, Texas, United States
    Posts
    105

    Default AC high temp switch not working

    Hello again.

    I recently replaced a boatload of AC parts in my truck. When I changed the accumulator it came with a new High temp switch. That switch doesn't appear to work. I had to change the pigtail also, and no matter which way I wire it the Compressor will not come on at all. I had to jump the two wires together so the compressor runs all the time.

    Any thoughts before I change the new High Temp switch? Anything I should check first? Doesn't removal of the HTS cause a severe mess with freon?

    Thanks
    95 Chevy Silverado
    Beat up by hail and a faulty tow truck
    5.7L V-8
    251,000 miles


  2. #2
    Sr. Engineer
    Join Date
    Aug 2009
    Location
    Virginia Beach, VA.
    Posts
    337

    Default

    After you did the accumulator, did you vacuum and re-charge they system??

    Sounds to me like there is no freon in the system

  3. #3
    Jr. Mechanic
    Join Date
    Apr 2011
    Location
    Wylie, Texas, United States
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    105

    Default

    Yes we evacuated and recharged. It cools fine; I just have to turn it off for a minute or two every once in a while to let it unfreeze.
    95 Chevy Silverado
    Beat up by hail and a faulty tow truck
    5.7L V-8
    251,000 miles


  4. #4
    Sr. Engineer
    Join Date
    Aug 2009
    Location
    Virginia Beach, VA.
    Posts
    337

    Default

    How much freon did you add back in??

    Sounds to me like your short some.
    If the line is freezing up, or the clutch doesn't engage (until it has sat for a while), then sounds like you are low.

    Once you crack the system, you should check the orifice tube, he can get gunked up over time.

    ---------- Post added at 12:53 PM ---------- Previous post was at 12:52 PM ----------

    I assume this is for your '95 truck.

    Does it also use the R4 compressor??
    Looks like this:: http://www.autoaironline.com/upload/...2%20Larger.jpg

  5. #5
    Jr. Mechanic
    Join Date
    Apr 2011
    Location
    Wylie, Texas, United States
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    Default

    This may be a dup post. Yes, it is an R4 compressor. I changed a whole lot of parts including the orifice tube, which was nasty gunked up. The AC has plenty of freon and works fine except I had to jump the two wires for the High Temp switch together to make it run. When I tried to wire it correctly the switch doesn't work. Its a new switch. There are two wires to it; I tried wiring it both ways. Neither one worked.

    It seems to me if the freon was so low that the compressor wouldn't kick on, it wouldn't run even with the switch bypassed. Isn't that true?

    Thanks

    Maury
    95 Chevy Silverado
    Beat up by hail and a faulty tow truck
    5.7L V-8
    251,000 miles


  6. #6

    Default

    Yes, it will run with the switch bypassed. The way that switch works is very simple. When there's enough freon pressure, let's say 30 PSI, the switch will close and allow current to pass through. It's just mechanical. Shorting the connector is basically doing the same thing. The A/C system doesn't actually know how much freon you have.
    ...
    ....

  7. #7
    Sr. Mechanic Ethan's Avatar
    Join Date
    Sep 2009
    Location
    Cedar Park, TX
    Posts
    150

    Default

    The High pressure temp switch allows the compressor to cycle, if that switch fails to work, the compressor will not turn on as a fail safe. Sounds to me like you bought the wrong accumulator, cause if you had to change out the pigtail, then it's defiantly the wrong one, AC parts should be an exact drop in replacement, and everything should hook up with no replacing of anything. All the connectors should be the same, if they are not, it's the wrong part.

    It's actually a low pressure switch, I don't know what I was thinking, but the same thing applies. When the compressor pulls the freon to a low enough pressure, the low pressure switch will break the circuit causing the compressor to kick off until it goes above the switches thresh hold. Bypassing the switch is not good, you need to get that fixed asap.
    Last edited by Ethan; 07-25-2011 at 03:48 PM.
    1994 Chevy Silverado 1500 Ext Cab 350 cuin TBI in dark Chevy blue
    160,000+ miles
    Original paint
    Original interior
    Original engine and tranny
    wrecked twice stolen once
    Diamond Plate bed rails
    Power windows
    Original Alloy wheels
    Original fancy smancy cup holder
    Tow package
    Original plastic bed liner
    K&N Cone Air Intake
    Dual MagnaFlow exhaust(not true dual) with chrome tips
    MSD Street Fire Performance Ignition coil

  8. #8
    Jr. Mechanic
    Join Date
    Apr 2011
    Location
    Wylie, Texas, United States
    Posts
    105

    Default

    Ethan, thanks for the reply. I have been too busy to reply or even work on the truck for a bit. I don't have the wrong accumulator; I had to get a new pigtail because like a moron I let the old one fall on the exhaust manifold and, well, you get the picture.

    I plan to work on it a little more as time allows as I get tired of manually cycling the AC, because I know it should not run all the time.

    Thanks!

    Stay tuned.... Power steering pump questions next!



    Quote Originally Posted by Ethan View Post
    The High pressure temp switch allows the compressor to cycle, if that switch fails to work, the compressor will not turn on as a fail safe. Sounds to me like you bought the wrong accumulator, cause if you had to change out the pigtail, then it's defiantly the wrong one, AC parts should be an exact drop in replacement, and everything should hook up with no replacing of anything. All the connectors should be the same, if they are not, it's the wrong part.

    It's actually a low pressure switch, I don't know what I was thinking, but the same thing applies. When the compressor pulls the freon to a low enough pressure, the low pressure switch will break the circuit causing the compressor to kick off until it goes above the switches thresh hold. Bypassing the switch is not good, you need to get that fixed asap.
    95 Chevy Silverado
    Beat up by hail and a faulty tow truck
    5.7L V-8
    251,000 miles


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