'91 240 Air con Mystery

Ramrodfunk

The air con in my '91 240 won't start.

I have replaced air con relay,condenser fan relay,Dash switch.With spares I had on hand after checking for dry solder joints,which I repaired if I found some.

Direct power to compressor clutch does activate clutch.

Bridging low pressure switch did nothing,even after lifting revs.

Checked fuses.

The light in the dash switch was previously working but has given up.I replaced the bulb with known working bulb.Still not working.

I know the bulb forms part of the circuit but I'm confused by it working before but not now after swapping out AC relay.

I pretty sure there is very little gas in the system if any but I believe bridging the low pressure switch would have a result.It did not.

I haven't tried the high pressure switch because I thought it would no effect without hi levels of gas in the system.

The air con uses R134a( I think,will check the sticker)

What am I missing??

I want to make sure it's going to work before going for re-gas.

Cheers

jamesinc

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Here are the full diagrams for you.

I think you should use a multimeter to look for 12V. If you look at the first diagram, you can see that the A/C switch should still illuminate even if the relay is broken or missing:

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So I think I would turn the car on and first check that you see 12V on both sides of fuse #12 (A), then check you have that 12V on relay (C) pin 15, and check you have it on the blue/yellow wire coming into the A/C switch (K).

The fact that you aren't getting the lamp to illuminate suggests that maybe there is a problem with the switch or the wiring between the switch and fuse or the fuse itself.

Ramrodfunk

jamesinc Thanks James. I'll have to watch a utoob video to remember how to use my multimeter.

I'll have a real dig behind the console tomorrow.

Has anyone ever tried to centralise the ground points for a 240 or centralise relay location? I'm thinking of a 740 relay "tray" behind my glovebox.

Cheers

carnut222

I've seen several of the blue snowflake rocker switches fail. You can easily test the switch, or if in doubt, just join the two terminals together and see if you get power to the compressor.

Ramrodfunk

carnut222 Never would have realised they could fail, just a simple switch. Would have been my last suspect. Cheers

jamesinc

If the switch is broken, send it my way, I sometimes can repair them

Ramrodfunk

jamesinc Woohoo, success. Got it going. i swapped out the control module(ECU). I'm not really sure if it was fault. I'll put the original back in it tomorrow to check.

Do you know a good A/C place around here?

I'll try a re-gas and hope there aren't any leaks.

Cheers

Ex850R

Ramrodfunk

You get a guy come to your place. Easy

jamesinc

Ramrodfunk I've used a few, if you want reliably top quality work, try this guy in Gladesville - https://maps.app.goo.gl/YU2YP9x2fkoxv4wX8

My usual guy is mobile. Marty, runs Mitrics. He's semi-retired and lives on the Central Coast, but he comes through Sydney regularly to do commercial AC work and will do cash-in-hand jobs around it, he can be a bit more difficult to organise but he's always been good to me. Call 0410 568 608.

carnut222

Ramrodfunk What "control module" are you referring to on the AC? AFAIK it's just a switch on the dash that powers the compressor, with a delay relay…pretty simple stuff.

Ramrodfunk

carnut222 carnut222 I only called it the control module because that's what it's worth referred to in the above diagram.

It's the ECU. but I put the old one back in and the air con still works. I'm still not really sure what was preventing it from working before but it may have just been me poking around and pulling connectors apart etc. that has got it working

carnut222

Ramrodfunk Yeah, OK I'd say swapping out the fuel injection ECU is unrelated to the functioning of the AC as the only thing the ECU does is command the pusher fan to come on if the engine temp is high. It won't prevent the AC compressor from kicking in.