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a/c charge low?


joeb

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My a/c compressor would not kick on last week so I decided to add a little bit of freon. maybe 3-4 ounces. I disconnected the battery and restarted the car and the a/c worked. than several days later it did the same thing. I added a bit more freon and as i was doing it i could hear the compressor cycling longer each time. from 50% on to maybe 80% on. i did not check it over the weekend since its my wifes car but I assume I have a small leak. why does adding 3-4 ounces seem to make it work? how low does the system have to be for the clutch to not cycle? 1/2 empty or more? at least it works but i have to figure out what exactly is going on.

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It's hard to say - the only accurate way to determine the amount of refrigerant in the system is to recover it, weigh it, and compare the weight to the system capacity. If the compressor is rapidly cycling, it is low. If the clutch won't engage, it is very low. Adding 3-4 ozs was probably just enough to pass the threshold where the low refrigerant code sets and disables the compressor.

To top off a system, I monitor the high and low pressure readings as well as vent temperature and compare the data to the performance chart in the shop manual.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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how low does the system have to be for the clutch to not cycle?

KHE,

I know the old piston compressors ran continuosly but don't these radials cyclce on and off even when fully charged?

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how low does the system have to be for the clutch to not cycle?

KHE,

I know the old piston compressors ran continuosly but don't these radials cyclce on and off even when fully charged?

The compressors on the Cadillacs cycle. I was referring to the system being so low that the clutch would not engage. If it is engaging and rapid cycling, it is probably low on refrigerant but that is not an accurate method of assesing the proper charge in the system.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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The beauty of an orifice-tube/accumulator system is that it will function adequately over a charge level range. The quickest method to assess the state of charge (if the ambient temperature is over ~70 F) is to put some load on the system (fan on high speed) and compare the evaporator inlet and outlet (accumulator end) temperatures. If the outlet is warmer than the inlet, add partial charge (say 4 oz.), allow the system to equalise, then re-assess the temperature differential. Once they're the same, add an extra 4 oz. refrigerant for reserve. When you think it's full, place a thermometer in one of the centre vents, set the temperature to 60 F, and go for a drive on the highway and see if the vent temperature drops below 42 F.

The problem with charging exclusively by system pressures is that the readings depend heavily on condenser temperature; it is next to impossible to simulate driving conditions on a stationary vehicle with an open bonnet. Underhood heat increases HVAC air inlet well beyond the normal range for a given ambient temperature, and the condenser suffers from reduced airflow and recirculation.

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I put in about 1/3 can on 4/9 to get the clutch to come on. it worked ok. cool, not cold. I stuck about 1/3 can in my other car. than I emptied the can into the caddy on 4/15. my wife said the a/c was working yesterday. If the clutch would not cycle on 4/14 than I can only assume I was very low. I think that I am still low but it is running. maybe another 1/2 can? the temp is not even close to 42deg.

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First of all, let's remember that the compressor has an overpressure release valve on it that will purge the system of excess refrigerent in the event you've overcharged it. Perhaps a low or high pressure sensor is falsely reporting excess pressure to the PCM such that it is prematurely shutting down the compressor.

You need to enter diagnostic mode and observe the Climate Control panel display to determine whether or not the PCM is commanding the AC clutch "ON." Now I'm foggy on this and others will have to chime in, but I think that when the fan icon is lit on the Climate Control Panel during diagnostic mode, that is an indication that the PCM is commanding the AC clutch to be "ON." (Could be ANOTHER icon ?!?).

If the PCM is NOT commanding the AC clutch "ON" then you need to look at PCM inputs. If the PCM IS commanding the AC clutch "ON" and it nevertheless fails to engage, then you need to look at relay/wiring difficulties related to the AC clutch circuit.

Regards,

Warren

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joeb: How does the top of the accumulator feel? It's the large aluminum canister on the passenger side. Is it ice-cold? If a low refrigerant code was set, I'd guess the system would need at least ~1.5 cans (~21+ oz). If adding more refrigerant doesn't decrease the evaporator outlet temperature or vent temperature, there's a possibility that something else is wrong.

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