A/C always on; bad dash switch? bad relay? How to Test? - Toyota Nation Forum : Toyota Car and Truck Forums


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Old 04-28-2007, 02:01 PM   #1 (permalink)
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A/C always on; bad dash switch? bad relay? How to Test?

I recently purchased a 2000 Camry CE, 4 cylinder with 105,0000 miles.

If I have the fan speed control on the dash turn to "ON", at any speed, the A/C system runs, whether or not the A/C button on the dash is pushed in.

The A/C button lights up when depressed and the light turns off when button is not depressed. The light dims when the headlights are turned on.

The A/C switch does NOT light up when depressed if the fan is turned to "OFF", which is what I have always considered normal behavior; i.e. no fan, no A/C.

There is the periodic increase or decrease in engine idle speed, what I consider as indicative of the compressor turning on or off. Remember this is with only the fan running -- the A/C button is not depressed. No change in behavior if I depress the A/C button, other the the button lighting up.

When observing the engine idle speed vary according to what appears to be the compressor starting/stopping, if I turn the fan speed control on the dash to OFF, the compressor cuts out and the engine speed drops. This appears to tell me that "turning off" the A/C this way effectively disengages the compressor clutch, so if correct, the problem doesn't rest with the clutch.

Air coming out of the vents is always cooler than ambient outside when temperature control is turned all the way cool. In the engine compartment, touching one of the pipes coming out of the compressor shows that the pipe is clearly chilled, another clue that the compressor is running; even if the A/C has never been "officially" turned on by depressing the A/C button on the dash.

Depressing the A/C button on the dash causes both fans on the back of the radiator to spin when the car is sitting at idle in the driveway. Turning A/C off via the dash button stops the fans. This leads me to believe that at least part of the switch behind the dash button is working properly.

So all indications appear to show that the A/C works fine, other than the fact that it seems to be always running with no way to turn it off.

My guess at this point is that something in the switch behind the A/C dash button isn't right, or if the switch is OK, perhaps some relay controlled by the switch is stuck on.

Is there anything else I can test to find out more information? Any hints, tips or other related advice would be most appreciated.

As a related aside, I note that when the A/C is running, I don't get that "A/C turned all the way down to cold might cause icicles to form" feeling that I do with my 1987 and 1996 Camry. I suppose there is the possibility that the 2000 is running a less efficient form of freon and therefore won't provide the same level of cooling, but that's just an uneducated wild guess and I only mention it in case it is a clue that means something to someone regarding the "is my A/C always on and why" question.

Last edited by ladd2; 04-29-2007 at 04:10 PM. Reason: edited title for greater clarity
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Old 04-28-2007, 05:10 PM   #2 (permalink)
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I'm not an expert on A/C circuits, but most have a relay controlled by that button. It may have multiple contacts or control other relays which do different things. ie- the switchlight, the cooling fans, and the A/C clutch. It sounds like the clutch or the relay or relay contacts controlling the clutch is stuck engaged. Perhaps start at the A/C clutch engagement wires and go back from there. Hope this helps. (But I'm just throwing it out there as my best guess.)
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Old 04-29-2007, 04:26 PM   #3 (permalink)
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Quote:
Originally Posted by Dave's
I'm not an expert on A/C circuits, but most have a relay controlled by that button. It may have multiple contacts or control other relays which do different things. ie- the switchlight, the cooling fans, and the A/C clutch. It sounds like the clutch or the relay or relay contacts controlling the clutch is stuck engaged. Perhaps start at the A/C clutch engagement wires and go back from there. Hope this helps. (But I'm just throwing it out there as my best guess.)
Thanks for the reply!

After reading your tips, I have revised my original question to include information that I think excludes the a problem with the actual compressor clutch. Your idea that the problem might be with some relay associated with the compressor clutch is good food for thought.

Prior to reading your reply, I spent most of the morning today pulling out the A/C control unit from the center console so I could get to the switch (and some burned out lights). A time-consuming job way more annoying than difficult given that one has to remove numerous parts from the right and left side of the dash in a particular order just to get to the inside of the center console so you can unhook a cable controling the "hot/cold" air mixture.

There is a possibility that the dash switch is not working properly according to the PDF I downloaded. On page AC-97, the guide says if the switch is depressed into the ON position, there should be continuity between pins 2 and five. My test shows there is no continuity.

Someone wondering why their A/C does NOT work might say "Aha! I need to replace the switch and that will allow my A/C to start working again".

Since my situation is that the A/C is ALWAYS working (if the fan speed control is on), I'm don't see how having a broken circuit on the switch (no continuity between pins 2 and 5) forces the A/C system into an "always on" mode.

I guess I could replace the switch (now that I have everything torn apart) and see what happens. A cheap fix for $50 if it works, but not the high point of my day if it doesn't ...

Anyone else have some tips or clues to offer re: the switch or possible relay?

Last edited by ladd2; 04-29-2007 at 04:28 PM.
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Old 04-30-2007, 09:08 AM   #4 (permalink)
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update:

There is a relay under the hood marked "Magnetic Clutch". According to various PDF manuals I have, this is related to the A/C circuitry and I could see how it might be possible that if the relay had failed in the "ON" position, it could explain why the A/C is always on.

The relay used in the Mag Clutch slot is identical to several other relays. I pulled the relay for the horn (same part number) and the horn stopped working. I put into the horn slot the relay pulled from the Mag Clutch slot and the horn again worked fine.

I'm not sure this test is definitive, but I'm thinking it is possible to conclude that the relay originally in the Mag Clutch slot works fine and therefore isn't the source of the problem with the A/C always being on.

I am currently unable to test the horn relay in the Mag Clutch slot, as I still have the main controls in the dash on the kitchen table.

I'm doing my homework here folks and could still use any advice, tips or clues you can offer!
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Old 04-30-2007, 10:46 AM   #5 (permalink)
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How many contacts are on the horn/clutch relay? It's possible for one set to become stuck(ie 'welded together') while the others are fine. Is it possible to assemble the switch enough to test everything without actually putting the dash together? You really don't need to connect the hot/cold cable, just adjust it so it's in the cold position. Then you could jumper between pins 2 & 5 and find if that's the problem. Cheaper than $50. Good luck.
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Old 05-01-2007, 08:48 AM   #6 (permalink)
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A shot in the dark?
Is your defroster on by any chance? With the selector in the defrost position, the A/C will run(by design)
HTH
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Old 05-01-2007, 03:46 PM   #7 (permalink)
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Quote:
Originally Posted by JerryR
A shot in the dark?
Is your defroster on by any chance? With the selector in the defrost position, the A/C will run(by design)
HTH
JerryR
That is certainly a strong possibility for a few of the situations I've noticed the A/C being on unexpectedly -- I usually start out in the morning with air blowing up onto the windshield so I get moving air yet it won't be directly in my face and this meets your criteria.

But I have also noticed the A/C seemingly always being on later in the day when using the main dash vents, so the defrost equals A/C on scenario wouldn't apply there.

I can't test that again now though as everything is all put back together and working properly -- and it may be a case of fixing a problem by taking everything apart and doing nothing but putting it all back together again.

Yesterday I was chatting with the Toyota Parts Guy at the local dealership about my problem; he was nice enough to ask one of the mechanics if he had any idea as to what to check. He suggested I see if the compressor clutch was somehow not disengaging, an easy thing to check. This seemed like a hot tip so I went right home to try it out.

The main belt goes around the outer wheel of the A/C compressor. This wheel spins around the inner wheel which is actually connected to the compressor, only turning the inner wheel when the clutches engage. So you can reach in (with the engine off!) and turn the inner wheel by hand and the only resistance you will feel is that of the compressor itself. If you cannot turn the inner wheel at all (or with great difficulty), that means it is locked to the outer wheel (clutches engaged) and no wheels will turn as the belt isn't turning. This would explain a scenario where the A/C was always on.

In my case, the inner wheel turned freely. I decided to check further and see what would happen with the inner wheel under the normal, engine running scenario.

With the engine off, I put a dot of white paint on the rim of the inner wheel. I put the inside center console heater control module back into the dash just enough to hook everything up electrically.

Started up the engine (with A/C button disengaged and fan off), looked into the engine compartment and could clearly see the white dot on the inner compressor wheel just sitting there motionless, with the outer wheel spinning around the inner wheel as the belt rotated it. Definite confirmation that there was no mechanical problem with the compressor wheels being locked together, causing the A/C to always run.

It suddenly occurs to me that if the belt is turning the outer wheel but not turning the inner wheel, that means that the compressor isn't running and there is no A/C. Doesn't this mean that the A/C is now no longer running all the time?

Push the A/C button on the dash and the compressor clutch engages and A/C mode is working. Push the A/C button on the dash again to turn the A/C off and danged if the A/C doesn't turn off just like it is supposed to. Button in and A/C on. Button out and A/C off. In/On, Out/Off. In/On, Out/Off.

I'll be danged to the lukewarms pits of heck. My A/C is working properly now.

I figure there are only two possible options -- either I was a complete doofus and completely mis-interpreted all my testing prior to spending hours figuring out how to take everything apart and then spending hours actually taking everything apart

OR

taking the A/C control panel apart and/or pulling various fuses and relays and putting them back in somehow remedied a bad connection

I'm going with the latter but won't bet the farm it wasn't the former.

For future reference to folks who are interested, on my 2000 Camry CE the two lamps that light up the heater control panel (fan speed, air temp, vent selector knobs) are NOT #74 bulbs as most people report -- they are JKL EWG103 and are Toyota Part 90069-98004. You can buy these bulbs online for $0.73 each plus shipping or pay $4.00+ each at your local dealership and they do NOT come with the little green condoms even at that exhorbitant price.

Last edited by ladd2; 05-01-2007 at 03:49 PM.
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Old 05-01-2007, 05:05 PM   #8 (permalink)
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Download the A/C service info and wiring diagram from the link below:

http://oregonstate.edu/~tongt/camry
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Old 05-01-2007, 06:11 PM   #9 (permalink)
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Glad you're working. And I'd bet the latter.
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