I have been trying to figure out why the A/C doesn't work properly on our newly acquired 240. So far I have determined with a pressure gauge that the freon was a little low and I added enough to get the low side running pressure to around 40 PSI.

The problem now is that the compressor cycles on and off rapidly. I tried bypassing the low side pressure switch as some suggested and that made no difference.

Then I used a sharp probe to check voltage on the compressor clutch wire at the white plastic connector under the intake manifold. Voltage is ~13 volts when the compressor is engaged, but drops to zero when the compressor disengages. So, I conclude that something upstream from that point is cycling on and off. Unfortunately the Bentley manual is no help at all on this.

I deduce that there must be sensors, switches, logic and one or more relays which determine when the clutch engage line is powered or not. Can anyone help point me in the correct direction? Is this a likely relay problem? Is there a circuit breaker in this line somewhere?

TIA for any help!

John

jthorner:

There are two pressure switches in the system, the low pressure switch, and the over pressure switch. Both of which can cause the system to cycle fast, especially if the pressure in the system is too high or too low. Excessively high pressure can be caused by two things (that I'm aware of... I'm not an expert), too much R134A in the system, or a plugged up orfice tube. Expect the plugged up orfice tube especially if the compressor is growling like it has bad bearings. If the compressor is growling, replace the orfice tube, accumulator, compressor, and flush the system to get all the compressor shavings out of the system. Then vacuum down and refill.

Sorry for the bad news, but the compressor on our 92 245 growled and cycled fast... not a cheap fix, but its been good ever since!

jorrell
--
89 244 171K miles, 92 245 236K miles, 06 XC70, 00 Eclipse custom Turbo setup

Hmmm, no growling, so maybe I'm lucky on that end.

Where is the orifice tube? The one diagram I've found of the system doesn't show it.

Thanks!
John