Air con compressor not disengaging

[V8 Power]

Noticed today that on my track car the air con pump is continuously engaged as in it does not cycle on and off like it does on our R3.
I do not think the clutch is the problem as if you turn off the AC the pulley spins freely.
It is as if it is not receiving the signal to cut in and out.
The air con is nice and icey cold.

Any ideas?

[warpc0il]

How much of the loom has been removed?



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[V8 Power]

None Dave

[warpc0il]

In that case you need to start fault finding at the clutch end. Either use an ohm meter to check the coil resistance or just put power across it and see if it operates.

There'll be a full diagnosis process in the Interactive Service Materials - Technical FAQ.

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[V8 Power]

Thanks Dave
The clutch is operable though as it turns on and off via the air con button.
It just doesn’t seem to cycle on and off like it should. Therefore I think there must be a fault with how the clutch receives its signal to do this.
I presume that is controlled by the pcm?
Is there anything obvious I should check for first?

[V8 Power]

The a/c system has a built-in diagnostic that is accessed by

With the REC/FRESH switch and the A/C switch pressed at the same time, turn the ignition switch to the ACC position, and wait for 3 s, then turn the ignition switch to the ON position and wait for 3 s or more while continuing to press both switches

The full procedure, and what the results mean are here
https://www.rx8ownersclub.co.uk/forum/v ... 58&t=35629
>Launch MAZDA Service Materials
Select "Troubleshooting" from the dropdown that default to Workshop Manual
> HEATER, VENTILATION & AIR CONDITIONING

[V8 Power]

That’s great
Thanks Dave

[V8 Power]

Ok I’ve worked my way through the troubleshooting and nothing matches my situation as there is not an actual fault, it is jus an observation that the compressor is not cycling on and off. It just stays on unless turned off.

What triggers the air con compressor to cycle on and off, Is it the internal car temperature or pressure within the system?

[V8 Power]

system pressure iirc.

[ChrisHolmes]

Try unplugging the connector next to the coolant header tank, cleaning it and replace. I think that a pressure sensor connection but am guessing.

[xamtex]

the switch chris is talking about has 2 sides...1 is a low pressure switch which stops the compressor when the pressure falls below a certain level,in the event off a leak for example. the oil that lubricates the compressor is carried in the gas...no gas-no oil--compressor seizes.
the other side of the switch is a high pressure switch which turns the compressor off if the pressure goes above a preset level to prevent damage...for example if the cooling fan fails...the system pressure rises very rapidly,ive seen the gauges hit 35 bar with no cooling and this can happen in seconds.
it is possible your system pressure is low,but not low enough to shut it down,so the compressor keeps running.
it really needs gauges on it to check what pressure its running at...and as with all a/c faults the first thing to do is regas the system properly.

[xamtex]

the pressure is dependant on the temperature...r134a only cools properly in a small pressure window...too high or low and it wont work properly...thats why it has its own radiator(condensor) and has fans blowing on it...the rad keeps the temp in the right window which keeps the pressure in the right window.

[xamtex]

there is a temp sensor on the evaporator which sends a signal to the pcm if it freezes which controls cycling aswell...to allow it to thaw then switches comp back on...
there is also an a/c amplifier i see in the curcuit from the manual..
the ambient air sensor also plays a role in how it all performs.

and just to complicate things its all controlled by the pcm..all these sensors send info to the pcm which makes everything happen.....or not.
as i said,it needs gauges to check pressures and regas as first step.

[V8 Power]

Thanks for all the input.
Some checking to be done.

[warpc0il]

Just to complicate things further, there's the cases listed above for the compressor to be switched on/off for ac reasons, but in the RX-8 the PCM also switches the compressor off/on at idle to help make the tick-over more even, and it drops the compressor when you floor the throttle, to reduce parasitic load for maximum acceleration.

For interest, it also does much the same thing with the alternator, only its load is controlled by the field coils rather than the physical drive, though the principle is the same and also impacted by temperature, battery state, etc.