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Testing the air conditioning compressor ??

AC/Heater 
9K views 17 replies 5 participants last post by  stokiedan 
#1 ·
I've finally decided to look into my lack of air con.
Had it gassed a couple of years a go, it lasted a month before it progressively stopped working so I assumed I've got a leak at the condensor (the obvious culprit)

As it's been a while since this happened I'd like to check the compressor is still functional. The compressor clutch isn't engaging at all now but as far as I'm aware the lack of gas in the system will prevent the compressor kicking in as the refrigerant is a lubricant for the compressor and its stops it working to prevent damage to said compressor.

Hope this makes sense. Bear with me....

Is there a way to test the compressor works without re-gassing ? Can I bridge a connection to activate the compressor so I know it's still functional (like you can with a radiator fan). Obviously only for a short burst as to not do any damage to it.

If this is a possible it might be worth while taking a punt on just swapping out the condensor + dryer before a regas as this is the most likely cause of a probable leak in my opinion. Ecp are about £66 for condensor + dryer at the minute so thought I'd give it a bash.

I've also got the updated relay already.
 
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#3 ·
theres a few ways i can think of, but all theoretical (ie: i've never actually needed to do it) depending which bit you want to test.

1) Find the low pressure switch and short the connector out (so it registers the circuit as 'good'). run the system as normal but not for longer than a few seconds.
2) If you want to test the clutch, then find the AC compressor 12v feed for the electro-clutch and whack 12v to it. should be able to hear/feel it engage/disengage. Possibly remove the alternator belt so you can spin the AC pulley by hand and you should feel some resistance when electro-clutch engages and works the pistons inside.

fyi, the AC gas itself isnt a lubricant, there is dedicated oil for that purpose but it gets injected when the gas goes in depending what parts have been replaced and/or oil comes out during re-gas.
 
#4 ·
Ooohhhhh thanks for the info. I'll deffo look into it :) I've had the Haynes manual out and it's pretty useless when it comes to the air con system. Maybe because it's illegal to release the refrigerant into the atmosphere at a guess.

I know naff all about air con. Didn't realise that about the oil. Might have a dig around see if I can find the 12v feed to the compressor. Might be the best bet :)

Thanks, much appreciated.
 
#5 ·
yeah, used to do a bit of AC in my spanner days (many years ago!). The oil is the bit why they recommend you run system every few months. while the gas is pressured so it's all around the system, the oil obviously settles into the low parts and doesn't get pumped around.

glad it's useful info. not that i keep upto date with FN2 common faults, but if it's not a common failure, i'll hedge my bets on it being a seal or a flex pipe at fault.
 
#6 ·
The compressor was working last time it was gassed and it progressively got less and less cold which indicates a leak somewhere. The only reason I want to check the compressor now is because it's been so long since it was last used.

It may be worth while getting it leak tested with the dye to see where this leak is before taking a chance on a condenser :)
 
#7 ·
Running an earth from pin for of the air con relay should engage the clutch which with a torch you can see running from looking from the top of the engine bay.

I had mine regassed about 2 years ago but it no longer works.
Did the shim on the compressor, still not working. Run the earth from pin 4 and it sprung to life but no cold air.. remove the earth and it's back to not working.. Relay replaced too..

I've got it booked in for air con service on Wednesday and if it doesn't cure it with a regass then I don't get charged.
But I suspect the compressor has failed/leaked..
 
#8 ·
These air con systems are quite the pain in the arse aren't they lol

I picked up a new condensor and dryer for mine today from euro car parts for £64. With mine working last time it was gassed and over the course of 2 months the air got less and less cold before there was no cold air at all I think I must have a leak somewhere.

Could yours be the same issue ?

I know nothing about air con but I've read theres a pressure sensor that senses pressure levels in the system and if the pressure drops below a certain level then it stops the compressor from engaging so it doesn't do any damage to it.

Reading your post then all I have to do is put a wire from that number 4 pin to the -ve on the battery and he clutch should engage on the compressor ?
 
#10 · (Edited)
So Diana is in the garage for the air con as we speak..

Either..
The gas just run low after 2 years and needed a Re-gas. £40 job done and working air con.

Or

They will establish there is a leak (which is what I suspect) and I won't get charged for the Re-gas and it'll be confirmed that there is a leak and if I'm really lucky, they will confirm what is leaking, all free of charge...
 
#12 ·
Cheers, and it all went swimmingly well! My car now has absolutely Baltic cold air con. Although of course we do now seem to be over our brief bit of sunshine we had last week...

I mentioned to the garage about the possibility of a leak and the guy said that the machine tests it all and if it finds that there is a leak then it won't charge the system.
 
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#15 ·
I had my system regassed there couple of days ago. The system worked great for a few days now it won't blow cold air. Asked at the garage and they said their machine didn't find a leak. He mentioned that the compressor could be leaking and this isn't running during the leak test. I'm now thinking I might replace the compressor.
 
#17 ·
The 'pressure test' normally done by AC refill places is merely a vacuum test which does not expose the o-ring seals to the same rigours as a proper pressure test (which is conducted with nitrogen). Many people are fooled into thinking their system is OK when it isn't.
 
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