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compressor ALWAYS on, has freon, but not blowing cold

camosilver on Sat February 28, 2009 8:44 PM User is offline

Year: 2000
Make: vw
Model: golf
Engine Size: 2.0
Refrigerant Type: r134
Ambient Temp: 75
Pressure Low: 35
Country of Origin: United States

i just bought a 2000 vw golf with the 2.0L non turbo engine, and even with the ac off, the clutch on the compressor is spinning. turning the ac button on, you can hear a click like normal and the change in rpm like the compressor has just kicked on, but it was already on! low side reading was 35psi, the air isn't even close to cold.

any ideas?

Edited: Sat February 28, 2009 at 10:11 PM by camosilver

Chick on Sun March 01, 2009 6:50 AM User is offlineView users profile

Are you sure you just don't see the outer pulley turning? Anyway, I would have the system leak tested, find and fix any leaks, then have the charge recovered and recharged into a deep vacuum the correct amount of refrigerant. If you can't find a leak, You might ask that some UV dye be added, and then you'll be able to leak check in the future. Your car uses a variable displacment compressor, so it will pump when low, and the common problems with those are either a leak, or a sticking control valve, but you will need to know you have the full system charge in there before diagnosing the control valve.. You also will need both high and low side pressures low side alone doesn't really tell us much, other than "some" refrigerant is in there.. Hope this helps..


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NickD on Sun March 01, 2009 9:14 AM User is offline

You have an idler pulley that is always spinning with the engine running, and the hub in front of that, that should not be spinning with the AC turned off. What about the gap between the pulley and the hub? Should be about 20 mils.

With the low side pressure, is it always 35 psi? Well let's talk about that gap first. But even without a gap, difficult to explain that click and engine speed reduction. Guess I do not understand your post.

camosilver on Sun March 01, 2009 11:06 AM User is offline

i know it doesn't make sense, the click and engine speed change, i have never seen anything like it before either, which makes it kinda hard to put into words. the clutch on the compressor is definitely spinning with the ac off. i do know the difference. i am not near the car to measure the gap, nor check the high side, but will do that as soon as i can.



Edited: Sun March 01, 2009 at 11:08 AM by camosilver

mk378 on Sun March 01, 2009 12:34 PM User is offline

First off you need to measure the high side to know what's going on. At 75 ambient, 35 psi static (which means it is measured after a long time with the compressor off, the high and low sides will equalize to the same pressure) means there is actually very little refrigerant.

This system has a variable displacement compressor. They can get stuck on zero displacement so they spin but don't compress. Before condeming the compressor though you need to be sure the system is properly charged and measure both pressures. Variable displacement compressor systems do strange things when undercharged.

camosilver on Mon March 02, 2009 11:54 AM User is offline

just got to the car this morning, turned it on and let it idle for about 5 minutes. high pressure side is reading 35 psi. it's now 50 degrees outside

dasinc on Mon March 02, 2009 12:49 PM User is offlineView users profile

If your low and hi sides are equal it means that the compressor isn't pumping. If the plate in front of the pulley is engaged and turning it would suggest a bad compressor. If the plate is not engaged and turning it's most likely a lack of refrigerant and a possible slow leak.

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TRB on Mon March 02, 2009 1:03 PM User is offlineView users profile

Equal pressures on a SD7V16 would lean more to a defective control valve in my opinion. We have seen post after post with this issue on this model compressor. That is if the vehicle has the proper refrigerant level!

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camosilver on Mon March 02, 2009 2:06 PM User is offline

what is the function of the control valve, and where is it located? what all is needed to replace it?

Edited: Mon March 02, 2009 at 2:32 PM by camosilver

TRB on Mon March 02, 2009 3:42 PM User is offlineView users profile

Page 5 & 6 in this PDF link.

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Chick on Mon March 02, 2009 5:05 PM User is offlineView users profile

Equal pressures can sometimes mean low charge, especially when the pressures are lower than the ambient temp..Sometimes a recharge to proper specs will bring them back to life, if not, you're better off changing the variable displacement compressor with new or reman. Changing the control valve on those is not as easy as on a GM.. Just my opinion..


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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

mk378 on Mon March 02, 2009 5:14 PM User is offline

I agree, 35 psi is too low: there is no liquid refrigerant in the system, only a few ounces of gas. If you have a leak detector use this remaining charge to check for leaks, then repair any leaks that were found, evacuate and recharge by weight. With a proper charge test again.

The control valve is inside the compressor. There was a guy here last summer who tried several times to open up his SD7V16 and replace just the valve, but it wouldn't work for him. It would've been better to swap out the whole compressor in the first place.

The control valve senses the pressure on the low side, when it is less than 20 psi it starts a process that causes the pistons to move less than their full strokes, which reduces the capacity of the compressor. This prevents over-cooling and icing the evaporator when maximum cooling is not required (low fan speed or cool ambient). I think the de-stroking process is driven by refrigerant pressure, so it doesn't work right when there is no refrigerant. Thus the need to test the system with a full charge.

Edited: Mon March 02, 2009 at 5:16 PM by mk378

TRB on Mon March 02, 2009 5:20 PM User is offlineView users profile

Agreed the Sanden is not an easy CV replacement compressor.

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camosilver on Tue March 03, 2009 9:55 AM User is offline

what should the low psi read? on most cars i have ever charged 35-40 psi on the low side had the ac blowing ice cold. i know you are supposed to do it by weight but just wanting to know what the pressure should read when i check it

Edited: Tue March 03, 2009 at 10:01 AM by camosilver

mk378 on Tue March 03, 2009 10:14 AM User is offline

The problem I'm seeing is that with the compressor off, the pressure should be a lot higher that it is. If you look at a pressure temperature chart for R-134a or the temperature scale on the gauge (this is the only time you use the temperature scale), the static pressure should correspond to the ambient temperature. If it is considerably lower, the system is nearly empty.

When you must charge by pressure, the high side is actually a lot more informative. But all bets are off with a variable compressor, those systems really need to be charged by weight.

bohica2xo on Tue March 03, 2009 12:27 PM User is offline

Trying to diagnose a refrigeration system without both high & low side pressure readings is like a blind man in a boxing ring... with Tyson.

If you are unsure of the compressor / control valve operation & condition, the system can be charged to a high side of 2x ambient temperature for evaluation. This does NOT mean that it is properly charged if you see cold air - it only indicates the compressor & control valve are working.
A proper charge must be measured by weight. The test charge should be recovered, and a full charge weighed in.

Since you just bought this vehicle, it may have had substandard repairs, sealant, repeated top-up charges, etc. If the compressor / control valve are OK, you should replace the dryer and add back some oil & dye. It is low on charge right now, so you will be chasing a leak.

B.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

NickD on Wed March 04, 2009 8:01 AM User is offline

If the pressure is that low and the compressor is still kicking on, sounds like somebody really played with that system and probably to get rid of that car.

camosilver on Fri March 13, 2009 5:20 PM User is offline

i bought a used compressor and took it to a shop and they said that one was bad too. it was doing the exact same thing though, where the compressor clutch is always on, even with the ac off. the only way we could get the clutch to stop was by disconnecting the plug at the compressor.

so obviously i am going to pick up another compressor, but do you think it could be anything else in the ac system causing the clutch to always be on? we were going to check the ac relay but apparently vw doesn't have a fuse/relay box under the hood(not talking about the one INSIDE the car) like most cars do for ac, starter, headlights, etc. apparently everything with the ac is controlled from one module, which is located on the back of the panel that houses the knobs for the ac and heat. BUT, i have the ross-tech cable that scans vw & audi cars(basically does everything the dealer scan tool does) and it didn't mention anything wrong with that module.

Edited: Fri March 13, 2009 at 6:09 PM by camosilver

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