A/C problems magnetig clutch engaging on its own

[xm 80]

so here's the problem I'm having the last couple of weeks with the AC compressor/clutch. if the car gets hot (after driving and coming to a longer stop at a traffic light) the AC clutch will engage and disengage on it's own!?!?

it doesn't happen when the car is cold (as far as I know). I noticed this, because the AC compressor makes a whining noice once engaged (could be a bad bearing or something similar).....well at the moment I don't care about the bearing of the compressor, I'm more worried about the weird acting of the compressor clutch.

so here's what I already figured out:

-AC works fine and still cools (even pretty good after all this years)

-AC Ecu seems to be working fine (I did the self test yesterday, and no error codes where present)

-checked the AC magnet clutch relay and it's also good (at least under cold condition, not sure if this changes after the engine bay is hot or the relay is hot, but shouldn't make any difference or?)

 

does anyone have an idea what else could be wrong with the setup?

[Scooter]

Isn't that just what it does normally? It cut's in and out as needed, the revs raise at idle is that what you are noticing and concerned about?

 

Is the system on 'auto'

[inazone]

Sounds normal to me.

 

 

[xm 80]

Isn't that just what it does normally? It cut's in and out as needed, the revs raise at idle is that what you are noticing and concerned about?

 

Is the system on 'auto'

not sure if that's a normal state...it just kicks in when ever it wants without me doing anything! no I'm not concerned about the idle, that is normal....it just doesn't make sense to me that the AC is turning on(the magnet clutch engages), on it's own.

I know my English might not be the best to describe this thing, but I hope you guys get it anyway

 

I was also thinking about this: what if the relay for the magnet clutch is faulty, but only if the engine bay gets hot....does this effect a relay at all?

[rider]

The compressor will cycle not on its own accord but when the pressure within the system attains a certain level. I don't know the specific settings to the Supra but the high pressure cycle on R134a in car air conditioning will be shut off on the compressor around 220psi and then come back on about 170psi if cooling is still required. At a steady state, off, it'll stabilise around 50 - 70psi across the system dependent on the ambient conditions on a properly charged system.

 

The compressor starting and stopping is what it does and is supposed to do.

[Ric]

The AC pulley does do this, it only turns (engaged) when it needs it, so it will start and stop.

 

As long as the AC is turned on, it shouldn't if it was turned off.

[xm 80]

The compressor will cycle not on its own accord but when the pressure within the system attains a certain level. I don't know the specific settings to the Supra but the high pressure cycle on R134a in car air conditioning will be shut off on the compressor around 220psi and then come back on about 170psi if cooling is still required. At a steady state, off, it'll stabilise around 50 - 70psi across the system dependent on the ambient conditions on a properly charged system.

 

The compressor starting and stopping is what it does and is supposed to do.

 

hmm ok.....so let me get this....if there's a leak in the system the compressor wants to increase the pressure in the system by turning on automatically?

is it possible to just unplug the fuse of the magnet clutch and drive around like this? I mean I don't really need the AC anyways, also been thinking of delete the whole system at some point.

[xm 80]

The AC pulley does do this, it only turns (engaged) when it needs it, so it will start and stop.

 

As long as the AC is turned on, it shouldn't if it was turned off.

 

 

not sure if I get this right Ric

 

so the AC pulley shouldn't turn if the AC is turned off?!?!

[Scooter]

The compressor cuts in and out to maintain the temperature you've selected.

 

The compressor has an outer ring that spins freely when it's off and when the aircon comes on the clutch engages and the inner part spins too, you can observe this by watching the pulley.

 

You can turn the aircon off inside the cabin, you probably have 'auto' selected hence the occasional cutting in, you could disconnect the compressor too if you wish, yes.

[xm 80]

The compressor cuts in and out to maintain the temperature you've selected.

 

The compressor has an outer ring that spins freely when it's off and when the aircon comes on the clutch engages and the inner part spins too, you can observe this by watching the pulley.

 

You can turn the aircon off inside the cabin, you probably have 'auto' selected hence the occasional cutting in, you could disconnect the compressor too if you wish, yes.

 

thanks for all the help!

so let's say if the temperature is set to the lowest possible position it'll still try to cool, even if the AC switch if in off position and the "auto" mode is not selected?!?!

[Scooter]

No I think you should be able to turn it off so that if the temperature was set low it just takes in air from outside and doesn't try and cool it further. But I'm guessing now, without the handbook or actually trying the buttons in the car.

[xm 80]

it's just strange....guess I have to look more into it. the thing is that I went on a 1,5 hour ride yesterday (it was nice and warm outside) without any problems at all! the only thing I changed was, I set the temp. to around 28°C...not sure if it'll happen again or if the problem has just been solved by unplugging and reinstalling the clutch relay or by just using the self test, but it was fine yesterday. so fingers crossed it sorted itself out anyway thx scooter for the help

[Ric]

The AC pulley does do this, it only turns (engaged) when it needs it, so it will start and stop.

 

As long as the AC is turned on, it shouldn't if it was turned off.

 

The outer ring of the pulley will always turn. But the central part should be stationary if the AC is off

 

When the AC is on, the inner pulley will turn when required also.

 

as described above.

[Chris Wilson]

The compressor will cycle not on its own accord but when the pressure within the system attains a certain level. I don't know the specific settings to the Supra but the high pressure cycle on R134a in car air conditioning will be shut off on the compressor around 220psi and then come back on about 170psi if cooling is still required. At a steady state, off, it'll stabilise around 50 - 70psi across the system dependent on the ambient conditions on a properly charged system.

 

The compressor starting and stopping is what it does and is supposed to do.

 

 

Sounds like you know refrigeration and air con !! Why is my Woods home dehumidifier freezing the condenser coils, starting and stopping according to room humidity, but not collecting water? I guess part of the cycle warms the condenser coil and the frozen condensate should drip off. It used to work fine, a tank full of water a week, it is quiet and I am attached to it. Fixable? Cheers.

[rider]

Sounds like its acting as a heat pump. That would only usually occur if the refrigerant flow is reversed as the pressure drop on the suction side of the compressor the other side of a capillary or valve is where the liquid refrigerant boils and cools. Does it have a winter heat pump setting on it?

[bebby]

Without trying to hack the thread, how do you self test the AC ECU as I've charged my system but it only lasts about 2-3 weeks, however when I do the vacuum test on the machine it comes up with no leaks?

 

 

 

[Chris Wilson]

Sounds like its acting as a heat pump. That would only usually occur if the refrigerant flow is reversed as the pressure drop on the suction side of the compressor the other side of a capillary or valve is where the liquid refrigerant boils and cools. Does it have a winter heat pump setting on it?

 

 

Hi, thanks for the reply, it doesn't have a winter setting, just a humidistat knob and a fast / slow fan speed. the fan seized and i freed it off and oiled it. Ice forms on the coil, but it doesn't seem to defrost and let water run into the container underneath. The thing cycles on and off, seemingly according to humidity though. It looks like a sealed system, is it probably best to scrap it? Cheerrs!

[rider]

Without trying to hack the thread, how do you self test the AC ECU as I've charged my system but it only lasts about 2-3 weeks, however when I do the vacuum test on the machine it comes up with no leaks?

 

 

/QUOTE]

 

Its nothing at all related to or to do with any ECU.

 

You are probably pulling what - 2 bar of vacuum? That's nothing compared to 15 bar operating pressure. If your gas is lasting 2 weeks good news is its a slow leak which could be a valve or union joint. First thing to bubble test is your service port valves under the blue or grey L and H caps (L is low pressure side and H, naturally enough is high pressure side). If they are fine then check all the union joints you can get to including at the back of the compressor. If they are all fine then you can add leak dye with oil to the system (charged with R134a propellant). You'll need a dark space and a uv light then to see where the dye is leaking.

 

There is a video that covers it - I haven't bothered watching it but it'll let you see what to do and check out.

 

 

Alternatively take the car to an a/c service garage or engineer to sort out. As always, care is required when working on the a/c system to avoid chill burns so safety goggles and gloves a must.

[bebby]

Its nothing at all related to or to do with any ECU.

 

You are probably pulling what - 2 bar of vacuum? That's nothing compared to 15 bar operating pressure. If your gas is lasting 2 weeks good news is its a slow leak which could be a valve or union joint. First thing to bubble test is your service port valves under the blue or grey L and H caps (L is low pressure side and H, naturally enough is high pressure side). If they are fine then check all the union joints you can get to including at the back of the compressor. If they are all fine then you can add leak dye with oil to the system (charged with R134a propellant). You'll need a dark space and a uv light then to see where the dye is leaking.

 

There is a video that covers it - I haven't bothered watching it but it'll let you see what to do and check out.

 

 

Alternatively take the car to an a/c service garage or engineer to sort out. As always, care is required when working on the a/c system to avoid chill burns so safety goggles and gloves a must.

 

Thanks for this, I was just wondering if the ECU could pick up where it started to get a lower pressure, that's why I asked.

I am a mechanic of trade but I'm more suited to power trains and hydraulics.

I'll check for union leaks because it worked absolutely amazing (when it worked)

Either way I'm not massively bothered as I very rarely us the A/C but i just want the car working perfectly

In regards to the vacuum test cannot remember exactly but the garage said there was no evidential leak present