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Another compressor question

 
Old 08-01-2004, 03:10 PM
  #1  
DaveK
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Default Another compressor question

My air con is suddenly not blowing cold air today. It did this a few times a year or so ago - and then would work again a few days later.

I don't think it's a leak - the compressor still engages suggesting I have at least some freon, and it was only charged a week ago. It wasn't leak tested - but it held a vaccum suggesting even if it did leak, it would be a slow leak.

The compressor is staying engaged a lot longer than usual - usually it cycles every 10-20s - but now it seems to stay almost permanently on.

My guess is - it's not working properly. The hose from it cools down a bit, but still feels tepid.

Is it possible the compressor has died, even though it engages? And can they be serviced?

I guess if it does turn out to be a leak I'll know in a few days because it will stop engaging at all.
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Old 08-01-2004, 03:13 PM
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John Boggiano
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No expert speaking here, but it sounds like a pressure loss (leak) to me, Dave.
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Old 08-01-2004, 04:20 PM
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Is it possible the outdoor temperature or humidity level affects your perception of how well it works? Have you cleaned the condensor (always step one before troubleshooting charge and other problems)?

If it really is an intermittent problem (not weather-related), try:

Is the condensor fan possibly intermittent, and that is causing your episodes of poor cooling?

You could have an intermittent problem with a mixing flap letting hot air into the plenum and mixing with the chilled air.

Your interior air temperature sensor and its fan - are they working? I think the vent on the CCU should hold a small piece if tissue paper if the fan is running.

If all else fails, read the CCU fault codes with a Hammer. I don't know about the 1990, but my 92 generates fault codes for almost every air conditioning component - all blowers and the mixing flaps are monitored, and a code is stored if anyone misbehaves.

A bad compressor is usually always bad, and quickly gets worse. I don't think the compressor will account for intermittent performance.

Good luck. I hope you get to the bottom of this soon.
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Old 08-01-2004, 06:11 PM
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DaveK
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I'm 100% sure it wasn't just my perception - it's definitely not blowing cold air. I know it's not interior fan / temp sensor / mixing flaps - if it was any of these it wouldn't explain the compressor staying engaged all the time (you can check the fan by feeling around the back of the CCU). It was only a few days ago I was watching the compressor (I am that sad!) and I know it usually cycles every 10-20s and that the pipe usually feels cold.

I'll check the condensor isn't blocked - but don't think that would explain the sudden change. The fan is on all the time.

From what you say - it sounds like it's not a dead compressor - so I guess John might be right. I'd be surprised though - it's changed very quickly which suggests a big leak - and yet, there is still enough gas to allow the compressor to engage, and it did hold a vaccum (although I guess the leak could be new due to the new charge blowing something).

I'll live with it for a week and see if the compressor stops engaging - or if it works again - and this will tell me if it's a leak or not. If it is, I'll get it leak checked. If it isn't - then I'm confused!
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Old 08-01-2004, 07:32 PM
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Not to Hijack this thread, but are you guys saying it is normal for the compressor to cycle every 10 to 20 seconds?

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Old 08-01-2004, 08:54 PM
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Randall G.
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Hate to say it, Dave, but sounds like a leak to me, too. When my A/C went from cold to no-cooling over a course of 1.5 years or so, the compressor went from frequent cycling to not cycling at all. I suspect the residual pressure was high enough to allow the compressor to engage, but there was inadequate R-134a for effective operation. If I had waited another year before charging, perhaps the pressure would have gotten so low that the compressor would no longer engage? Sounds to me like you're thinking along these lines, too.

You should be able to pick up a cheapy gauge that allows you to check your low-side pressure. It's real easy to do....

Lon...I don't really have a quantitative answer for how long the compressor should run between cycles. Though, I do know the compressor on all 3 of my cars (including the new one) cycles. And, that the compressor must eventually cycle, or the evaporator would freeze up. Oh, and that I wish I had a dollar for every time I've heard the compressor engaging ("click") on the brand new car sitting next to me at the stoplight.

I would suggest just measuring your center-vent vs. ambient temperature, preferably after the car hasn't been superheated by sitting in the sun. If the center-vent temp is within spec, I wouldn't worry about the compressor cycling.

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Old 08-01-2004, 09:31 PM
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Colin 90 C2
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Dave,
It sounds like you need to hook up a gauge set to the compressor and see what your high and low readings are and if they are holding steady or fluctuating.

The readings will give you the best idea as to the state of your entire system.

I would think that your local a/c shop may help you out with a diagnosis, possibly free of charge.

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Old 08-02-2004, 04:28 AM
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OK - so I guess the obvious question is..... if I get it pressure tested, what should the pressure be?

And if I did it myself - what sort if gauge do I need? A special air con gauge? A tyre pressure gauge (I suspect this wouldn't fit!)?
Which connector on the compressor is the low pressure?
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Old 08-02-2004, 08:57 AM
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I've just been out in the car at lunch time and I notice I have a noise when I switch the a/c on. It's kind of a whistling noise (although it doesn't sound like gas escaping).

I think it's coming from the luggage compartment. It sounded like it was coming from down behind the petrol tank (where the evaporator is I guess).

Is noise normal when you're low on charge?
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Old 08-02-2004, 09:08 AM
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Colin 90 C2
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Dave,
You will need air conditioner gauges.
The low side is the valve that is pointing to the rear of the car and the high side is the the valve that is pointing to the oil tank.
As for the pressures, these figures are approximate but you'll get the idea.
At 30 deg C the low side should read between 9-15 psi and the high side should read between 230-270 psi.

If you pressures are within the range and are steady then you have other problems.
It could be that your mixing flaps are not adjusted correctly or a host of other problems.

Try to get your pressures checked first.

Good Luck,
Colin
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Old 08-02-2004, 10:52 AM
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For what its worth Dave, I just had mine checked by the dealer, sounds similar to your problem......I need new evaporator & pressure hoses. I saw the price of the parts, so just got mine recharged....hoping will last till the end of the summer!

I believe you can have the rubber hoses replaced & use the original fittings.
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Old 08-02-2004, 11:18 AM
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Randall G.
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Dave,

One more point with respect to checking the system pressure. The readings are with respect to the compressor running. If you just walk up to a cold car and hook up the low-side gauge, you should get some high reading (60 psi or higher) if you have a decent amount of refrigerant in the system. You may have a hard time locating a high-side gauge that fits, considering that it really needs a 90 degree head with the tight quarters. Just having the low-side gauge is a real good start, and (in the US) you can find 'em in any generic auto parts store.
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Old 08-03-2004, 03:20 AM
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OK - I thought it was unlikely I'd get air con gauges at our local car store so I went to get the system pressure checked. This was not by the guy who recharged it but somewhere I knew was fairly local.

In fact, they didn't pressure test it but persuaded me that since it's leaking, it may as well be recharged with dye. So they vaccumed the system out (only 175g came out) and refilled it with some lovely dye. (It was slightly worrying when they opened the luggage compartment to get to the air con ports though.....).

I'll give it a week or so until it stops working, then I'll take a look and see if there are any obvious leaks around the compressor, pipe joins above the rear wheel, condensor, receiver / dryer. If I can't see anything I'll let them try with the UV light. And if we still can't see anything I may have to conclude it's the evaporator after all - and just start opening the windows.
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Old 08-03-2004, 09:29 AM
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Colin 90 C2
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Dave, since the system is supposed to hold 930g of freon, then you obviously have a leak. I don't believe that you will see much leaking without the uv light and tinted glasses. I would suggest you run the a/c as much as possible with the fresh charge so you can make any small leaks detectable.

On the bright side, this is a good time to switch to r134a if you have not already done so.

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Old 08-03-2004, 09:33 AM
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Already R134a. It's interesting you say 930g - my mechanic told me 850 which is what I told the guys last night.

I suspect I won't see it either - but the place I used yesterday said that if it was a major leak then I might be able to. I plan to keep the air con on most of the time (although I can't today because my girlfriend borrowed the car and she hates air con). Once it's failed I'll check the connectors anyway - might as well because I need to take the covers off the wheel arches for them to shine the UV light in there anyway.
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