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1999 TDI Aircon stuffed. How to diagnose.

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1999 TDI Aircon stuffed. How to diagnose.

Postby rebuilder86 » Fri Nov 16, 2018 5:31 am

Hey all
1999 VG 2.5 Tdi Transit SWB.
come back from overseas for 2 months and its frikn hot here in Perth and my aircon isnt working.
Im poor and theres no chance of giving it to somoene to diagnose.
The clutch isnt getting 12 volts.
I cant find anythign except an aircon fuse in the cabin. No relay marked aircon. EVery car ive ever had has had an aircon relay.
I can jump the compressor clutch to the battery and make it turn but theres no cold air.
Am i correct in assuming there is some kind of auto disconect switch which turns the compressor off if there is a freo problem?
So perhaps i just had a gas leak and now theres no gas, and therefor the compressor doesnt even bother turning on?

Am i on the right track?
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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby rebuilder86 » Fri Nov 16, 2018 5:38 am

I just pressed a punch into the fill port and there was abig burst of freon so i dont think its empty. I woudve thought if there was a leak, the entire thing would be close to atmosheric pressure.
no?
At what sort of pressure would the system stop supplying 12 volts to the compressor.
I should also point out, whne i jumped the clutch, it made absolutely no difference to engine rpm, whcih sort of sais to me theres not enogh in the system to compress.

Perhasp the gas is fine (indicated by teh burst of freon) and the problemis the pressure switch? IF so why didnt it get cold when i jumped the compressor?
IS there a second thing that the switch operates other than the compressor? like perhaps it opens and shuts a valve door in the evaporator housing, or turns a nother blower fan on and off?
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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby knobby1 » Fri Nov 16, 2018 5:50 am

There is normally a high and low pressure switch....if the pressure is outside the specified limits, high or low, she won't work.

I suspect you may have low pressure...but without plugging a proper AC test kit into it or getting someone who knows about these things ....we shall never know.

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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby Airthies » Fri Nov 16, 2018 10:23 am

+1 on the low pressure
One way to check but it's not conclusive is find the pressure switch and check continuity across terminals. Depending on how it works it will be on or off (I suspect on-has continuity) when system is ok.
But you would be best with wiring diagram to be sure which way round it works.


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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby rebuilder86 » Sat Nov 17, 2018 3:23 am

Ok so i guess the pressure switches would be the only things i can test.
A turbo diesel should drop rpm a bit when aircon compressor comes on shouldnt it?
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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby knobby1 » Sat Nov 17, 2018 8:47 am

rebuilder86 wrote:Ok so i guess the pressure switches would be the only things i can test.
A turbo diesel should drop rpm a bit when aircon compressor comes on shouldnt it?


Mine actually gains 150-200rpm at idle when the air is on, but being a Mk7 it has an electronic throttle control.

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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby Jim Archer » Sat Nov 17, 2018 10:27 am

Not sure the EPIC injection raises the idle any - just compensates for the load, but you should hear the engine note change when load increases, similar to easing the clutch in with no throttle applied in traffic.

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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby andz327 » Sat Nov 17, 2018 9:29 pm

If its got electric cooling fan or fans ,make sure they're working and not seized in case it's same idea as mk7 if fans not working the ac compressor wont kick in

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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby rebuilder86 » Sun Nov 18, 2018 4:18 am

Yeh the thermo fans are turning on. It must have just had a very slow leak. I guess i ust thought a leak would normally empty the system.
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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby amlav » Tue Nov 20, 2018 9:54 am

had a small crack on one of the ac aluminium pipe on mine . Had to take it off and blow air in to it to be able to find it .
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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby MinorMatt » Tue Nov 20, 2018 8:35 pm

If it has a leak... shine a UV torch over all the components and the location should be obvious
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Re: 1999 TDI Aircon stuffed. How to diagnose.

Postby rebuilder86 » Fri Nov 23, 2018 3:59 am

so the only thing these switches control is the cluthc then right?
there is one on the condensor, and one on the line from the heat exchanger to the evaporator.
i guess they both have to be at a certain pressure before they give continuity to the clutch??
Anything else they control?
Ive jsut triedsplicing into the wire to the clutch so that when i jump it its also powering everyhing back down the wire that might also get power when the switches are in continuity, but still, even with that, there is no cold air.
There was some refrigerant. surely it would all leak if there was a leak? its been 6 months
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