Testing A/C compressor?

JustAnotherSaver

I think my compressor is goosed. The A/C was working until a week or so ago and then stopped. I no longer see the inner wheel on the compressor spin when i engage the A/C and the system does still have gas as i've tested the kPa.

http://www.megavaux.co.uk/Upload/ProductPart/9474e-13124749_air_conditioning_compressor_astra_h__zafira_b_ident_wg.jpg.jpg

That link looks pretty much like my compressor.

I was told to test the plug to see if it's receiving 12v. That is beyond me, i've no idea how to test it but i can ask the garage at work if they'll do it tomorrow as they should know how.

Question really is whether i can safely disconnect that plug or will there be a problem (regards the gas in the system)?

I imagine it should have 12v. If the compressor needs changing does anyone have an idea how long it should take a garage to do?

m_c

And what was the kPa reading?


It's far more likely to be either a lack of gas problem, or something else causing the AC to be disabled, than a compressor fault.

Geoff1963

The gas in the system will only come out if there's a leak, or it vents on over-pressure ; unplugging the electrical connector won't cause it. The plug will only get 12 volts when A/C is on, and the engine is running, so it's a bit tricky.

Get hold of a wiring diagram, and see if there's a relay. If there is, hold a finger on it while someone runs the engine and selects A/C on and off every few seconds.
That will tell you if the problem is : control ( gas pressure, evaporator temperature sensor, ECU etc. ), or power ( fuse, compressor, under-bonnet wiring etc. ).

If the system gradually loses gas, it will become inefficient ; but as the pressure drops, so does the leakage, so it will look as though there is some.

A new one will probably take an hour or two to fit - a main dealer can give you a quote. It will cost several £100s.

JustAnotherSaver

Are we talking a few £100 for fitting or the part? As I would just chance a second hand one tbh I think. I only plan on keeping the car another 4-5 years.

The kPa reading was either 420 or 520 I can't remember which. While not the highest it's ever been it was certainly much higher than it was when I actually did have a leak before I had the front rad thing changed which name I forgot. I bought a genuine Vaux one back then. Ever since then the A/C has been spot on and even a couple of week ago was working fine.

bobbymotors

It's more likely to be a faulty pressure switch

AdrianC

Frankly, if you don't even know how to point a multimeter at a connection to check if there's +12v, then you're probably just best off asking the garage why your aircon isn't working, and letting them figure it out. Chinese Whispers, and a waste of their time/your money is bound to result if you micromanage something you don't understand.

Iceweasel

Before condemning the compressor I'd be checking the fuse, the switch, and the relay first.

AdrianC is right - let an AC specialist check it out.

m_c

On anything modern, the AC is likely to be electronically controlled, so you can't really test much without a computer. Gone are the days of it simply relying on a couple pressure switches to decide what to do. Modern systems will often have various other dependencies.

Provided there is gas in the system, the next step would be to check to see what whatever module that controls the AC is actually doing, which if it's a AstraH/ZafiraB as per your link, IIRC the engine module will be responsible for working the AC, but it'll be dependant on getting the correct request from the Climate/Body module.

khcomp

Unless you have the ability to use a meter and test the pressure switch, clutch switch, etc. then it's a job for a garage: I wouldn't recommend assuming that a component is faulty and just replacing it by guesswork - in the case of the compressor, you'd still need to have the system evacuated and purged prior to removal of the old unit and regassed after; it's possible to regas it yourself with a DIY kit, but I doubt you have the kit to safely extract the old gas.

JustAnotherSaver

For the benefit of those who think i'm going to jump in with both feet and diagnose tonight...

I'll happily admit i don't really know anything about these things and i'm even worse with electronics than i am with mechanics.
With that said there is an on-site HGV garage where i work and i get along with the manager there. He was going to test to see if there was 12v at the plug (as advised as step 1 online) but other things came up and we'll have to do it another day.

I would've come back with the outcome and see what step 2 would be. This test wouldn't have cost me a penny.

So if i can do that, if i can get the tests done and rule things out or even hopefully find the cause of the problem ... for free ... then surely that's a good thing?
Another thing could be - if i take it to a garage then they could say it's XYZ when the chap i'd have had tested it would've said XYZ is working perfectly fine, in which case someone is telling porkies maybe, and since the guy i work with isn't making money out of me you'd think it'd be the other guy.

So surely there's no harm in it, right?

I never said i was going to just jump in right at the start and say i'll replace the compressor. All i said is i would chance a second hand one since i've seen new ones go for a few £100 .... as in if it's the compressor that needs replacing then i will chance a second hand one, but until that stage i'm not buying anything, only testing.

AdrianC

A second hand compressor is quite likely to be dead, especially if it's been off the car for a while, even if it was working before the car was scrapped. Seals dry out when it's out of use, which is why cars that haven't had the aircon used over winter tend to lose their gas very quickly in the summer.