Another AC problem


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Old 05-13-07, 11:03 AM
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Another AC problem

1999 beetle. The compressor will not cycle unless the rpm is 21-2200.

I've added one can of 134, when it does cycle it's good and cold so I don't think I should add more..

I'm thinking a bad pressure switch maybe..?

Any thoughts?

Thanks!
 
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Old 05-13-07, 11:25 AM
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Ya, you're on the verge of overcharging the thing.

I presume the compressor is running but merely contiue to run until you run the engine up to 2000+rpm. Am I correct?

That is typical of an avercharged (or nearly overcharged system.

If a system is low on freon, it will cycle rapidly at an idle. If it is on the high side of charge or even overcharged, it will not cycle at all at idle but generally will at higher engine speeds.

An overcharged system or an undercharged system will not cool well. There needs to be the correct amount of freon on the system to allow a predesigned pressure differential between the low and high sides so there is proper expansion of the freon as it passes through the orifice or expansion valve.

too little freon and the high side can't build enough pressure.

too much freon and the low side can't get low enough to allow for the expansion.
 
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Old 05-13-07, 03:42 PM
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Thanks nap.

Does the same apply with 134a as with R-12? This is a 134 system.

The odd thing is the AC worked but wasn't really cold and the compressor would cycle at idle, before I parked the car for about a week.

I just added one can of 134a. I thought maybe there was a leak.

I can also hear the refrigerant gurgling in the firewall when the compressor is on.
 
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Old 05-13-07, 07:12 PM
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r12 and r134a both perform the same function and are close enough in performance that 134a is a direct drop in replacement for an r12 system.

I tend to do "by ear" charging in most of my vehicles. I charge until the compressor cycles very slowly to not at all at an idle but when revving it will cycle.

Basically what you have now but you need to be careful not to go too far or it becomes overcharged and actually provides less cooling.

Not knowing where you started is why I said the overcharge part. Many folks that have other problems often simply keep dumping refrigerant into the system.

so, depending how often it would cycle off and on at idle, it may or may not have been low.

as far as gurgling; are you sure it is the refrigerant. Generally it doesn;t gurgle but is a constant release of pressure, kind of like letting the air out of a tire type sound. If a v dub has an expansion valve (offhand I don;t know if it does or not) you would get a less consistant sound from the expansion point but still generally not what I would call gurgling. Sometimes I have heard it as a groan but generally can;t hear it while the car is running.

So, is there really any problem or was it just the concern of the lack of cylcling of the compressor?

If it is cooling well, I would just let it be. If it isn't cooling, we'll keep going.
 
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Old 05-14-07, 07:30 AM
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There is a problem. No AC at idel but good cooling at 21-2200 rpm.
I could alway get compressor cycle at low RPM until now.

That gurgle is connected to the AC somehow, I'm pretty sure of that. I only hear it when the compressor runs, if sitting inside the car.
 
 

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