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Low Charge (On Purpose)

timber on Thu August 15, 2013 10:07 PM User is offline

Year: 2002
Make: GMC
Model: Sierra
Engine Size: 6.0L
Refrigerant Type: 134a
Ambient Temp: 106 F
Pressure Low: 51 psi
Pressure High: 295 psi
Country of Origin: United States

Hi,
I'm a licensed HVAC contractor, but new to automotive.

The above measurements were taken at a idle of 800 rpm.

Compressor, condenser, accumulator, metering device and a high side hose replaced.

Leak tested, flushed, 8 oz of PAG 46, evacuated to 400 microns for 2 hours.

Weighed in a charge of 18 oz

OEM charge calls for 29 oz.

Normal cruise speed rpm is 1800-1900. At this driving range I get a 45-47 degree F at the center supply register with 106 F outside. Compressor stays engaged at all times except for acceleration, which I think is normal.

I'm afraid to add more refrigerant, to bring system up to OEM specs, with the pressures and temps that I have now.

Does anyone in Arizona run a 'low' charge to compensate for the high ambient temps that we have?

Any ill effects on the compressor?

mk378 on Thu August 15, 2013 10:12 PM User is offline

Without a full charge all the oil tends to pool up in the evaporator, which is bad for the compressor. Always use the specified charge amount.

High side getting too high is typically because of inadequate condenser cooling. On a full size truck with engine driven fan, the fan clutch can be worn out. Fan will still spin but not as fast as it ought to. Triple digit weather will stress any system though; being over 300 on the high side in such conditions isn't necessarily abnormal.

Edited: Thu August 15, 2013 at 10:15 PM by mk378

timber on Thu August 15, 2013 10:49 PM User is offline

Thanks,
Temps have dropped to 100* F and I added the remainder of the ref into the system. It did not change the low or high side pressures, so I assume that the ref is being stored in the accumulator.

Leggie on Mon August 19, 2013 3:35 PM User is offline

Quote
Originally posted by: timber
Hi,



Normal cruise speed rpm is 1800-1900. At this driving range I get a 45-47 degree F at the center supply register with 106 F outside. Compressor stays engaged at all times except for acceleration, which I think is normal.

It is especially normal for fixed displacement compressors as the output is directly related to shaft speed. It doesn't cycle nearly as often on variable displacement compressors which controls the output much like an alternator.

You can check the fan slippage by marking the fan side and shaft side with white fingernail polish and observing it with DJ ing type strobe light. You would see the two halves moving relative to each other if there's slippage. If this checks out ok, unbend the fins, remove rocks, debris and wash the condenser. The car is 12 years old and normal washing don't really get the condenser, so its due anyways. I like Berryman B-33 foaming engine degreaser for this purpose as it sticks very well and does not smell like diesel fuel like most engine degreasers.

As you're aware, starving the system of refrigerant interferes with proper operation of the metering device.

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