A/c clutch not engaging

[Brentenorris]

Ok guy's i have searched for over a month now and can not figure this out. My compressor will only engage when pins on the relay have been jumped or 12v to the compressor wire its self. The things i have tried is a different accu, ecu, mpi relay, all new relays under the hood, compressor, by passing dual pressure switch and a numerous ac switches in the cabin. A pressure of 170 on the high and 38 on the low i'm at a loss.

 

[DSM1G90]

How about the button on the dash. Is the yellow and/or green light come on. How about the fan switch...when you hit it to first click, do the lights come on depending on which position the button is pushed in .. which is first push, "economy (yellow)", and the second push "full (green" ?

Let's start there since you've already mentioned 'cabin switches' ...

 

[luv2rallye]

Well I'm an electrical guy, not an ac guy. But looking at the diagrams I can see what you need working for the magnetic clutch is: dual pressure switch, engine coolant temp switch, ECU, and magnetic clutch relay. For the rest of the ac to work (fans & regulation) you need a working: ACCU, air inlet sensor, air thermo sensor, ac switch. And for the blower to work: blower, heater relay, blower switch, blower resistors, blower motor high relay.

 

[Brentenorris]

Well the ac switch is good. Fan kicks on and the air inlet sensor and air thermo sensor, engine coolant temp sensor are all in spec.The accu is good. Magnetic clutch works when bv is applied. I have also tried two different ecu's. You can jump the pins out in the ac fuse box under the hood and the compressor will come on and work fine.

 

[luv2rallye]

It's engine coolant temp switch, not engine coolant temp sensor.

 

[MikeSD]

this may be a stupid question, but you have tried all the hard stuff, is there enough freon in the system to engage the clutch?

 

[luv2rallye]

He's shorting the dual pressure switch to simulate freon being there (proper freon pressure would close switch). Since that didn't work he's trying to find why the magnetic clutch still won't engage.

 

[turboglenn]

mine did thi last mon5th, low on coolant,can't kick on with lo pressure, iput some in and found the leak, one condensor newer and i had AC again, blew my trans the nest day

 

[donniekak]

Have you tested the ac control unit? Its in the dash behind, and above the glove box.

 

[Brentenorris]

Luv2ralley thats what I meant was switch. Sorry about that.The accu is good I have 2 that where put in a 1g with a working system and they functioned fine. The freon is correct, there is 28oz of refrigerant in the system and thats with a vacuum on it before freon was added. Is there anyway to check the ecu driver that controls the ac and fuel pump relays? I have also tried 2 different ecu's.

 

[luv2rallye]

Yes the engine coolant temp switch is a totally different component than the engine coolant temp sensor. Are you sure your 1g accu is compatible with the 2g one? You said you were bypassing the dual pressure switch so having freon in won't matter. If you don't bypass the switch then you must have the correct freon pressure and a working switch.

Why are you concerned about the fuel pump relay when you're trying to get the ac working?

Do you have +12v on the ac compressor clutch relay's green-red wire with all ac stuff turned on (or bypassed)?

 

[Brentenorris]

Luv2ralley The dual pressure switch is being bypassed. Sorry again about the misinterpretation. I have two 1g accu's not a 2g accu. On page 24-6 of the 1g back up service manual it mentions the mpi relay after the accu on the heater and air conditioning trouble shooting. I'm assuming you are able to see what I am? That's what makes me think the mpi relay is involved. By the way I'm going to snow shoe west va. with my buddy and his 2g tsi fwd rally car on the 25th -29th of this month

 

[luv2rallye]

Sorry I was looking at 2g diagrams (I answer so many posts every day it gets hard to remember to always check if it's a 1g or 2g).

I see no mpi relay on page 24-6. But it must be working to power most sensors and solenoid valves in the engine bay, injectors, IAC and also the ECU. So check if you have output voltage from it.

The better diagrams to look at are on page 8-101. Do you have +12v on the magnetic clutch relay's green-yellow (green-red was for the 2g sorry) wire with all ac stuff turned on (or bypassed)? And near 0v on it's red-black?
If so, do you then have +12v on it's white-red? Then if relay is working you should get +12v on it's black-white.

 

[Brentenorris]

I have battery voltage on the green-yellow. Then I have battery voltage on the red-black wire. Why would this need near 0v? Then I have battery voltage from the white-red wire then the black-white wire has -02.1

 

[turboglenn]

I went through all this same sh1t for a week, jumping it and it would work, do yourself and the foprum a favor buy a 20 dollar bottle of AC refil, and run tthe car with the AC turned on and i bet the AC pump starrts running once there's some pressure in there..keep it till it's about full, themn shut the car off with the AC left on and listen for the leak as you most likely have on.. mine was fromthe P/Scooling line rubbing the condensor

 

[luv2rallye]

Then I have battery voltage on the red-black wire. Why would this need near 0v?

Because to activate the magnetic clutch relay the MPI control unit (aka ECU) pulls this line low (see p. 8-101). So the ECU is not pulling this line low either because it's bad, or more likely (because you said you tryed another ECU) some input to the ECU is not proper (like perhaps the engine coolant temp switch), or maybe a wire is broken/not connected.

You can verify that the magnetic clutch relay turns on the compressor magnetic clutch by temporarily touching a ground on the red-black wire (it won't damage the ECU).

 

[Brentenorris]

Turboglenn the a/c has the correct charge and it's not leaking down. My next thing is locate another ecu and try that. Is there anyway to check the ecu to see if the ecu is pulling the voltage like its supposed to?

 

[luv2rallye]

Only by installing one and measuring that voltage - but you can measure it at the magnetic clutch relay. Remember it may be some input to the ECU (that it needs for ac) isn't correct OR the ECU itself.

[Note you're reading battery voltage on the red-black wire because the ECU has that wire shut off (open circuit) so the voltage comes through the relay from the other side.]