Compressor damaged?

Hi, My car air-conditioning was not working so I had an air-conditioning expert look at it. He said there was a bit of gas in it and so did a leak test with Nitrogen. It held pressure and so he said there was no leak. The compressor clutch was not engaging so he said I needed a new compressor which would be about £400 pounds to replace, I told him I didn't want to spend this kind of money.

I bought a second hand compressor cheap and connected a car battery to the two terminal lead and it drew a lot of current and the lead got hot very quickly. I measured the resistance and it was a dead short. I measured the resistance on my fitted compressor and it measured 3.5ohms, better I thought, I then connected a car battery to the lead, it drew a lot of current wires got hot and I heard a fizzing noise. I then measured the resistance again, this time it measured a dead short.

I thought the clutch was operated by an electromagnet, maybe this should have been pulsed with a short duration of voltage and maybe the engine should have been running to hold the clutch in.

Does anybody on this forum know the technical internal workings of a car A/C compressor to shed some light on this?

What make, model and age of car is it?

These magnetic clutches require power to them any time you want them energised. I thnk its about 4A for the 12V ones but i may be thinking of the 24V ones on trucks/busses so it could be 8A.

Are you applying power to the correct connections? some compressors have a thermal fuse which is designed to blow if the compressor get too hot.
If you existing compressor clutch fails to pull in despite having power to it, with the engine OFF and the clutch energised push the clutch plate with a stick so that it touches the pulley, does it stay pulled in? If so the air gap is too big due to wear for the magnetic field to pull the clutch in and will need a new clutch. If the coil is gone you may be able to get a new one.
If either compressor has been open to the air for more than a few minutes it'll need fresh oil putting in before using again, the oil is very hygroscopic.

monkey spanners

The car is Peugeot 406 HDi 110bhp year 2000.
The 3.5 ohms I measured would equate to 3.4A so probably was the correct connection, but now it has gone short-circuit it draws mega amps!

Quote:

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Originally Posted by homebrew

monkey spanners

The car is Peugeot 406 HDi 110bhp year 2000.
The 3.5 ohms I measured would equate to 3.4A so probably was the correct connection, but now it has gone short-circuit it draws mega amps!

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Strange. I'm not to familiar with car AC. Is it possible the coil has a spike voltage protection diode built in? In that case did you apply voltage with the correct polarity? Is it a separate ground wire or is the coil grounded through the compressor body?

SteinarN

Hi, that is a very good point I was not careful with the polarity!
I don't think the coil is grounded through the body because I just looked at an internal picture of the compressor and the coil wire terminates in a 2 pole connector.

As Monkey says the clutch sounds like it is fried.

You should be able to get a replacement clutch for the compressor without a major problem.

You 'expert' is taking the cheaper/easier option as it is quicker to change over a complete compressor than to strip off and replace the clutch.

It is a task you could possibly do yourself if you feel up to it.

You need to check that the compressor is free to rotate before going any further though. A new clutch and a seized compressor is a waste of money.....

Some of the vehicles I worked on had a sensor somewhere that if the compressor suction got too warm the clutch would not energize at all.

I don't know if that may be the case with yours, but I thought I would throw in some comments just in case.

I would be a bit worried about your "auto A/C EXPERT" if he can't diagnose the difference between a bad clutch or low on refrigerant.

Ken

Quote:

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Originally Posted by TXiceman

I would be a bit worried about your "auto A/C EXPERT" if he can't diagnose the difference between a bad clutch or low on refrigerant.

Ken

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I didn't like to say that out loud ;)

Brian, I am from Texas and we are not real bashful here...Just get what is stuck in your craw and spit it out.

Ken

SteinarN

You was right I had fried the spike protection diode that is built into the lead to the compressor's coil. On removal of the shorted diode I connected a battery to the compressor coil and the clutch pulled in.
I will need to get the system gassed because the "expert" removed this when he did the compression test.
Does anyone know where I can look to find the relay or switch which operates the coil voltage?

You could try your local Peugeot dealer for spares :) - just a thought ;)

Quote:

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Originally Posted by homebrew

Hi, My car air-conditioning was not working so I had an air-conditioning expert look at it. He said there was a bit of gas in it and so did a leak test with Nitrogen. It held pressure and so he said there was no leak. The compressor clutch was not engaging so he said I needed a new compressor which would be about £400 pounds to replace,

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All this could just have been low gas due to leakage over the winter period.

Most Car A/C have a low pressure switch connected to the compressor clutch.

If the pressure is too low it just won't pull in untill the pressure rises. You can hear these click in when static charging vehicle A/C.

If you don't regulaly use the A/C once a week or so for a few minutes over the winter period vehicle A/C can leak via the numerous rubber gasket joints which dry out through lack of oiling from refrigerant flow.

When pressure testing systems that have leaked some of their charge over winter they usualy pass a OFN pressure test as once a system has been operated again for a while the re-oiling of the joints seals it all up again!

It's just a quirk of vehicle A/C apparently.


I bet if your 'expert' had just re-charged with the correct amount of 134a (probably around 750-850 grams) then it would have kicked in fine!

:p

A lot of the pressure switches used on vehicle airconditioning systems are of the 'trinary' type. A single switch senses both low and high system pressures in the low side.

Firstly... Was there 12 volts at the clutch leads when the system was charged? If yes, then the clutch was duff, if no then then have a look at the trinary switch mounted on the lower left hand side of the condenser and see if you are getting 12 volts to there or not, a new pressure switch should be around 30 quid from auto air gloucester, a bit cheaper than your pug dealer.. They are a cinch to change as the system does not need to be pumped down as there is a schrader valve under the switch.. If the switch is OK , then you'll have to get the wiring diagram out and trace the wires out as I can't find mine.

The pug 406 is fitted with a Sanden SD7V16 compressor and has a nasty habit of suffering from clogged displacement control valves, and the condensers are garbage... Check closely the lower pipe connection as they corrode badly and leak..

RE:Peugeot 406HDI year 2000

Homebrew,

I see you've had lots of good advise here and as I see it's still work in progress and that you are fairly 'hands on', I'll add my own comments if I may:

If your compressor field coil is still OK, your are right, the current draw is approx. 4amp at 12volts. If you reverse the polarity, the quenching diode should be capable of frying a 10 amp fuse momentarily. (A faulty diode could harm the ECC)
Hopefully, you are able to re-use your old compressor and have now checked that the magnetic clutch energises when fed a 12volt supply (with correct polarity:)? If possible, drain out the old oil and check the cleanliness of the ports.
Replace or refit 'O' rings and lubricate them with a little clean oil. Tighten hoses.
Look at the a/c condenser (the radiator immediately behind the front grill), can you see any oil stains? The majority of cars of this age would have salt corrosion to the condenser and vulnerable to leaking.
Good practise would be to change the receiver drier filter.
Check the fuses! There will be a fuse for the a/c (it may perform other functions as well)
Have a/c recharged: Ask for UV Dye and compressor oil (PAG oil) to be added (to replace oil drained earlier).
With refrigerant pressure in the system, the pressure switch will operate.
Now it's time to cross your fingers and toes!
If a/c does not now operate, there will be an electrical fault which could be any of the following: fuse, relay, pressure switch, wiring harness or connector, a/c switch/temp control or ECC fault. Fuses and multipin connectors are favourite, but hopefully it won't come to this!

Hope some of this is helpfull.

hi mate i'm a qualified auto a/c engineer you're right the vehicle a/c clutch is served via electro magnet and should pull in once power is placed providing earth is in place,sounds like clutch magnet is knacked to me,,,,
hope this helps , cheers trev

Quote:

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Originally Posted by homebrew

SteinarN

You was right I had fried the spike protection diode that is built into the lead to the compressor's coil. On removal of the shorted diode I connected a battery to the compressor coil and the clutch pulled in.
I will need to get the system gassed because the "expert" removed this when he did the compression test.
Does anyone know where I can look to find the relay or switch which operates the coil voltage?

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You will want to replace this diode rather than just clip it out. It catches the back emf from the clutch winding to protect the auto's electronics from transient spikes.

Thanks for all the replies.
I have replaced the diode I had fried and the clutch now pulls in okay and the compressor is not seized.
I therefore went to Qwik-Fit and had the system re-gassed (10 days ago). Worked great and I measured the temperature on full blast and it was 11.5degC.
The system has since got progressively less effective and now the air is only slightly cooled even on full blast, must be a slow leak I think.
The "expert" had used his ultraviolet torch to check for leaks and found nothing. (Last summer the system had been re-gassed with dye to find a big leak, turned out to be the Condenser which I replaced).
Any ideas anyone?

dirty evap? or condencer? Clean coils go a long way!

The 406 is quite prone to leaky condensers, the lower fitting corrodes quite badly sometimes to the point where the hose needs to be replaced.. Could even be the condenser itself, there are a lot of cheap parts on the market at the mo and corroding through within 12 monts in not unheard of... the compressor was second hand.. was it any good when you bought it? leaky shaft seal? poor connections..

So the Kwik Fit expert recharged you without a leak check?... Another blow and go..;)

Karl,
I changed the lower hose last year with the condensor because it had corroded on and I had to peel it off. I did not use the second hand compressor because the one on the car still worked.
The Kwick Fit process is fully automated and the first thing it does is compress with Nitrogen and check for a leak. Last year the air conditioning only lasted a few weeks but I did not need it because of the lack of summer!
Could there be a leak on the low pressure side, hence a very slow leak?

Yes there could be a leak absolutely anywhere.. I don't find UVdye very useful on a car, I use a decent electronic sniffer followed up with leak detector spray. For condensers I use a strong mix of coil cleaner in a garden sprayer.. The only real use for UV dye is for shaft seals which may seal when the compressor is not rotating... Look for the splash marks round the engine bay in line with the compressor. It takes time and patience but I always find my leak :D