Air Conditioning

[Ozzyal]

G'Day All,
I've got an interesting issue with the A/C . I've been doing a rebuild on this P38 over the last 12 months bringing it all up to spec. The A/C has been checked over, serviced, gassed and lubed. The issue is the compressor turns on runs for a very short time and switches off. Comes on again briefly and switches off. Pressures are all fine. Has anyone has the same issue and found what was was causing it?
Cheers, Al

[old dirt bikes]

Hi Ozzyal, when you say the pressures are fine, could you please give the actual pressures in PSI or KPA. Also could you also let me know the ambient temperature and humidity at the the time of testing. Your problem sounds like it could be a faulty pressure switch or maybe the evaporator temperature sensor. Regards,
Alan

[Scouse]

Voltage drop at the compressor clutch and an excessive air gap are the most common causes of intermittent A/C when all else has been checked.

Land Rover introduced a relay into the circuit with a new harness incorporating a load resistor. Have a look in the engine bay behind the LH headlight for the resistor. It's gold in colour and approx. 5cm long IIRC.

The compressor clutch wears over time & the air gap becomes so large that the clutch magnet can't hold it engaged. There's a shim behind the clutch which has probably already been removed by now so the only fix now, if the air gap is too big, is to either replace the clutch or file/grind down the clutch boss to get it closer to the compressor.

[prelude]

What is the load resistor used for?

I ran into the same problem a few years ago and just ran a positive wire straight from the battery to a relay and disconnected the positive from the compressor to the coil of the relay and that has been working like a charm ever since. I am not loading anything up with a resistor though...

Indeed check pressures and post them if possible, also check the temp of the evaporator, it shuts down the AC when around 4c iirc. Also, check the pressure switch when the AC is running and after it has cut out.

Cheers,
-P

[Scouse]

What is the load resistor used for?

As far as I can tell it's just there to fool the HEVAC unit the same way one fools the indicator flasher unit when fitting LEDs.

[prelude]

Ahhh I see, well, a standard automotive relay draws up to 200mA and I never had an error in my HEVAC unit. So it might be needed, might not be. I guess since the heavy load causes the voltage to drop (I think thermal protection or something?) and the clutch to not engage a lower current draw is actually needed in my case.

Anyway, that's just my experience.

Cheers,
-P

[Ozzyal]

Thanks lads,
That's very good info. In a month or so when we have some warmer weather I will head down those rabbit holes and see what I find.
Trying to sus out aircon issues in Vic winter/spring is fairly self defeating [biggrin]

Alan
Torquay, Vic