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More '93 240 A/C Questions - Electrical

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

Reply to
John Horner
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I'd exercise some caution at this point. Go and burn up the compressor and you'll have compressor debris spread throughout your system and need to start replacing major components.

Do you have R134 or R12? If R12, i'd consider doing an R134 conversion with new oil, expansion valve, drier.

To me if the compressor just started working with a little freon added, you have enough to cycle but not enough to meet requirements. Go and add the wrong amount of freon and you'll fry your system. Cycling the compressor is bad for it and over filling will kill it.

You need to decide what you have on your hands and where you want to go. If the freon was low, there is a reason for that. maybe just dried o-rings, or maybe a leak.

On my 1987 740 I had a drained system and R12 system. While the system was dry I did an R134 conversion myself, replacing all o-rings, new drier and expansion valve, draining and refilling the compressor. My plan was to replace all of this and address leaks as needed. Oh, I flushed the condensor too.

Be careful just jumping in and trying to get it running on the cheap -- it may cost more down the road.

John Horner wrote:

Reply to
Jamie

Reply to
fastblue

A correction to my post, I ment low inside cabin temperature and switch set to minimum and be carefull not to overfill with freon! I ruined a compressor on a chev truck that way. Also check this post

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As far as the cycling goes, it's controled by the air conditioner knob

Reply to
fastblue

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