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Volkswagen Compressor Cycling

JCBrewer on Tue July 08, 2008 2:59 PM User is offline

Year: 1998
Make: VW
Model: Cabrio
Engine Size: 2.0L
Refrigerant Type: R134a
Ambient Temp: 90
Country of Origin: United States

Hey all! I've got a pesky VW Cabrio that isn't keeping me cool anymore. I like to go top down, but sometimes in Alabama in the summer time that just isn't very comfortable.

Thing is, the compressor is cycling. It comes on for about a second, then is off for two. It blows colder than ambient but not much. And I'm guessing it isn't doing the compressor a lot of good to cycle like that.

Do any of you experts have any experience with this system? It would be the same one as on the Golf, Rabbit, Jetta, and probably Passat of the same years.

Thanks much!

U-96 on Tue July 08, 2008 3:57 PM User is offline

That's exactly what my compressor was doing (1995 Golf, must be almost identical A/C systems) when stupid me overcharged the system in an attempt to revive it. Luckily for me the compressor was already not operational, so I did not cause any further damage.

mk378 on Tue July 08, 2008 4:05 PM User is offline

Check that the condenser fans all work. If someone has been messing with it, it could also be overcharged as U-96 said.

JCBrewer on Tue July 08, 2008 4:24 PM User is offline

So the problem was an overcharge?

The A/C worked fine last year, but it hasn't been working this summer. So I don't see how it could be overcharged. I was thinking that perhaps it has a partially clogged expansion valve that is causing the high side pressure to spike and the overpressure switch keeps turning it off.


JCBrewer on Tue July 08, 2008 4:25 PM User is offline

Are the condenser fans just the radiator fans? They are working properly and it is cycling even on the highway at speed where the fans shouldn't even be running.


bearing01 on Tue July 08, 2008 4:36 PM User is offline

The drier trinary switch will kill the compressor clutch if head (high side) pressure gets above 464psig. With the system then off once the pressure falls below 348psig the switch will let the compressor kick back in. If you think it's a high head pressure problem due bad air flow over the condenser or an over charge then spray the condenser down with a garden hose, while the AC is running. That will efficiently take the heat out of the condenser and make the head pressure lower. But to really see what's going on you need to look at the high side pressure.

The compressor will also kick off if the (high side pressure) drier trinary switch pressure falls below 17.4 psig (it should normally be around 200psig). With system off, if the high pressure again rises to 34.7psig then the switch will close to enable the compressor again. If this is the case then, with high side pressures that low you either have no refrigerant in the system or you have a blockage. I don't recall if the drier trinary switch is on the inlet side or outlet side of the drier. If it were on the outlet side then you may have a blockage in the drier. With the system running if you can feel a difference in temperature between the hoses running in and out of the drier then there's a blockage in there. That could cause the system to suck the drier outlet pressure down below the 17.4 and kick off the compressor. Another check is to feel the small diameter pipes / hoses running back to the expansion valve. If the compressor is cycling and the drier tubes are cool to the touch then you have a restriction there. All the small diameter tubes & hoses (the liquid lines) should feel hot around 100'F or more.

Edited: Tue July 08, 2008 at 4:39 PM by bearing01

Chick on Tue July 08, 2008 8:07 PM User is offlineView users profile

You will need to get the pressures. You could be overcharged (providing someone added some) or undercharged, due to am leak. Pressures are needed.. Hope this helps..

PS: if someone added anything, try to find out if they also added sealer..That is not a good thing....

Email: Chick


Freedoms just another word for nothing left to lose

JCBrewer on Wed June 03, 2009 4:16 PM User is offline

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