Variable compressor on constant system?

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Motohead1
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Variable compressor on constant system?

Post by Motohead1 »

I have an odd one for the experts here. I have a mechanical variable compressor off a 2004 passat running in 2001 dodge dakota that is a constant displacement system. I have been running it that way for years with no issues but for a quick clutch cycling when at idle. I have a shrader valve leak on the low side so I need to pull the system down to replace it. But while I have it empty to replace the valve I was thinking that maby an orifice tube change could help with the idle cycling? Any thoughts? I have no idea what the stock orifice tube size is on the dakota.
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JeremyB
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Re: Variable compressor on constant system?

Post by JeremyB »

Sounds like the low pressure cutoff switch is set to high for the control valve in the compressor?

With a variable compressor, it shouldn't be cycling at idle at all. I'd try and disable or lower the LPCO switch and with some gauges on and see what it does.
Dougflas
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Re: Variable compressor on constant system?

Post by Dougflas »

just put a decent cap on the low side and do not pull the charge just to change a schrader. Schaders are not the sealing but a cap is there for sealing.
Motohead1
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Re: Variable compressor on constant system?

Post by Motohead1 »

So I pulled the stock dodge orfice and it was all but blocked. Compressor was starting to come apart. BTW stock Orfice was orange so .57. I put a purple in there .72. New dryer and compressor (denso) and flushed out everything. Its getting about 52*F coming out the vents now but it will still cycle at idle. Serviced up to 1.81lbs and 7 oz of PAG 45 as thats what the VW compressor wanted. (Dodge was PAG100) Gauges off its 95psi. Running at idle low is in the 40psi range and high it will climb up to 150psi before hanging out there a bit and cycling off for about 15 sec. Much better than with the old .57 tube. Could it be over serviced causing the cycling?

Jeremy you mention low pressure cutoff. Can you tell me how the switches work on the system? I thought the Low press switch on the dryer is to make sure there is pressure in the system and the high pressure side switch is for over pressure cutoff. Is that correct? I have no idea what the PSI triggers are for both. the Compressor is a denso 471-1374. Its mecaniccly variable as there is no solenoid controlling it. No sure what parameters it uses either I imagine PSI?
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JeremyB
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Re: Variable compressor on constant system?

Post by JeremyB »

Forum ate my comment a few days ago and has been having server issues since then.

With a constant displacement compressor, the LPCO switch is what keeps the evaporator from freezing. It 'monitors' the low side pressure (and by corollary temperature) and shuts off the compressor before the refrigerant gets to the freezing point of water.

With a variable displacement compressor, the control valve regulates low side pressure. The compressor starts at 100% stroke until the control valve reaches the set point pressure (and by corollary temperature)

With your system, you have two competing low pressure controls in your system. Disabling the LPCO switch should keep it from cycling at idle.
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Tim
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Re: Variable compressor on constant system?

Post by Tim »

JeremyB wrote:Forum ate my comment a few days ago and has been having server issues since then.
Moved to a new server. Propagation will take a day or so. Some data was lost between the daily back-ups. We tried to get the most recent file at the time.

Both ackits.com and this site seem to be stable on my end.
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