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Compressor short cycles

dwg on Sun February 24, 2013 6:29 PM User is offline

Year: 2005
Make: Lexus
Model: RX330
Engine Size: 3.3l
Refrigerant Type: R-134
Ambient Temp: 40
Pressure Low: 31
Pressure High: 200

I noticed the compressor was only running for a few second at a time on my RX330 .

It is winter here, and the A/C was working fine last time we used it. So not sure when this problem started. Only time a/c runs is for defrost.

I put a set of gauges on it, and initially, when the compressor was running, the lo side started ~40-50 and when the compressor kicked on, it would immediately head down to 30. Then the compressor would kick off. Hi side starts at ~95 and has reached about 110 by the time compressor kicks off.

I figured it is low on gas. I have added one 12 oz can of 134, no oils or sealer.

With that one extra can in there, when compress kicks on low side still cycles from 50 down to 30 then compressor kicks off.

Hi side starts at 200 and runs up to 250 by the time compressor kicks out.

I am confused. I thought it was a low-pressure condition causing the compressor to cut out, but evidently, that was not it. I have never put a set of gauges on it before, so I am not sure what normal is.

My next idea is to get a schematic and find out what is causing the compressor top kick out. I see a pressure sensor with four leads, which I assume is a hi/lo sensor.

Any other ideas?

mk378 on Sun February 24, 2013 7:43 PM User is offline

This sounds normal. In cold weather there is no need to run for a long time, since there is no heat to move. It should be cycling on evaporator temperature, and when it is already 40 it only takes a few seconds to get down near 32-- where the compressor must stop or it will ice up.

It appears now you have severely overcharged it. Modern systems seldom take more than 24 oz from completely empty. The days of just throwing a can in to see what happens are over.

Edited: Sun February 24, 2013 at 7:47 PM by mk378

dwg on Sun February 24, 2013 8:00 PM User is offline

I never noticed the compressor kicking in and out like this before. It runs for 2-3 seconds, then off for 20-30 seconds, then back on for 2-3.

Are you saying this is normal?

GM Tech on Mon February 25, 2013 9:03 AM User is offline

perfectly normal at 40 degf ambient

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

dwg on Mon February 25, 2013 10:45 AM User is offline

Now that I have "fixed" my perfectly normal condition by adding 134, what sort of damage control needs to be done?

Does this need to be taken to a shop ASAP to be recovered and correctly charged or can it wait until spring, to tell if it is working or not? What harm does excess refrigerant do? Just poor performance, or is damage being done?

Dougflas on Mon February 25, 2013 5:10 PM User is offline

You could disconnect the plug leading to the compressor and wait for warm weather. The best thing would be to recover the charge and properly weigh in the correct amount. This way, when you need the tempered air for defrost, you'll have it.

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