Aircon Fault

[Forrest]

After being parked up since February, I now find that the aircon in my 1997 CD Estate is not working. Will check the pressure at the service port over the weekend but I suspect it has leaked. I have voltage at the low pressure switch and if I bridge that switch briefly the compressor starts to run.

A few specific questions.

If the system does have pressure and I then suspect the pressure switch is that replaceable without evacuating the system? I am sure I have read about them being fitted via some kind of Schrader valve but it looks more like a straightforward screw fitting.

Where have folk found the most common places for a leak to be? I'm assuming the O-rings on the condenser is one of the first places to look. Anywhere else?

Finally, if it transpires the system is empty, has anyone used nitrogen to pressure test? If so, how? I see there are cheap N2 cylinders available for welding. What sort of pressure are these filled to? Nitrogen is supposed to be better than compressed air because of the need to keep moisture out of the system. I'm assuming one would need a regulator on the cylinder to do this safely.

Thanks for any tips.

[Clan]

Originally Posted by Forrest

After being parked up since February, I now find that the aircon in my 1997 CD Estate is not working. Will check the pressure at the service port over the weekend but I suspect it has leaked. I have voltage at the low pressure switch and if I bridge that switch briefly the compressor starts to run.

A few specific questions.

If the system does have pressure and I then suspect the pressure switch is that replaceable without evacuating the system? I am sure I have read about them being fitted via some kind of Schrader valve but it looks more like a straightforward screw fitting.

Where have folk found the most common places for a leak to be? I'm assuming the O-rings on the condenser is one of the first places to look. Anywhere else?

Finally, if it transpires the system is empty, has anyone used nitrogen to pressure test? If so, how? I see there are cheap N2 cylinders available for welding. What sort of pressure are these filled to? Nitrogen is supposed to be better than compressed air because of the need to keep moisture out of the system. I'm assuming one would need a regulator on the cylinder to do this safely.

Thanks for any tips.

I would leave it to a professional as the law changed in 2010 , only certified Automobile AC engineers can do maintenance to vehicle AC Systems now. Most Technicians in garages now will have these qualifications. The max fine for willingly letting AC Gas out into the atmosphere is £40,000 .
Pressure is no indication of volume of gas in the system, the only way to check that is extract the gas, then do a leak test with nitrogen gas, fix the leak then put back the correct weight of the liquid gas.

The 940 was always very robust regarding leaks and the most likely place for a leak in any car is the Condenser. It may well need a conversion kit to use the later R134a gas.

[Forrest]

The car was R134a from the factory. It’s reading about 5psi with the engine having been off for 24 hours. This suggests to me that it has been/is leaking badly but as Clan says probably still has some refrigerant in it so is indeed not in a suitable state for DIY troubleshooting.

With the engine/compressor off the pressure should equalise across the system meaning the low pressure test port should read higher than in normal operation. I’m thinking in excess of 50psi, possibly much higher.

I shall try and find time to look at the condenser over the weekend. I’m guessing there could be tell-tale traces of oil near any major leak.

My reason for wanting to understand this fault is not because I have it in mind to try to fix it myself. I do not have the equipment or certification necessary to do that. It’s just my experience with using professionals to work on old cars is that you tend to get a much better result if you can point them at the probable cause.

Thanks for the input. Will keep you posted.

[volvo always]

On my 1996 940 with AC. Non working when bought in 2016. Over the last year finally have working AC.

Look out for dark staining, or dampness. Check all the AC pipes and rubber hoses.

Leak points have been the Condenser. New Nissens brand fitted perfectly. Old condenser clamp a pig to remove. Hope the bolt head on yours snaps off! O rings on clamp to condenser. Clamp No Longer Available. Well pleased when bought a used one as well as better used AC pipes.

AC compressor leaking. £30 used compressor fitted.

The shrader valve itself. Needed tightening.

Since last Summer finally holding it's charge.

You would be best to get a AC specialist out as have better equipment like a sniffer tool. Replace the Orifice valve only £4 in the pipe on the chassis rail and the receiver dryer canister, as may be old and if leak absorbed moisture. Canister on mine came with the O ring seals. NRF brand. Orientation different, original rubber front pipe connects to the right on new dryer, but works great.

If you get your AC evacuated by the machine, your average garage should be able to replace the condenser themselves with new O rings. Would imagine a lot cheaper. Then call specialist out to evacuate again, pressure test and if ok, refill.

If you can I would buy any used AC 940 pipework as spares for the future as well as the Condenser clamp. Quote for compressor refurb was expensive at £150+vat years ago. Just got lucky with a used one. Kept old as spare to refurb.

Good luck with it. James.

[Clan]

Originally Posted by Forrest

The car was R134a from the factory. It’s reading about 5psi with the engine having been off for 24 hours. This suggests to me that it has been/is leaking badly but as Clan says probably still has some refrigerant in it so is indeed not in a suitable state for DIY troubleshooting.

With the engine/compressor off the pressure should equalise across the system meaning the low pressure test port should read higher than in normal operation. I’m thinking in excess of 50psi, possibly much higher.

I shall try and find time to look at the condenser over the weekend. I’m guessing there could be tell-tale traces of oil near any major leak.

My reason for wanting to understand this fault is not because I have it in mind to try to fix it myself. I do not have the equipment or certification necessary to do that. It’s just my experience with using professionals to work on old cars is that you tend to get a much better result if you can point them at the probable cause.

Thanks for the input. Will keep you posted.

There is very little difference in the AC system between your car and a brand new one today.. the faults as few as they are, are easy to find with their equipment.