Need AC help !!
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New User
Joined: Jul 2010
Posts: 4
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Need AC help !!
Good Morning!!
I just had the good fortune of buying a 1988 F250 Diesel (IH 7.3 non turbo) from an older couple - few miles, always garaged and always dealer serviced. It hasnt been driven muvch in the last few years and has only 67K miles.
The air conditioner isnt blowing cold. It was converted to 134a by the dealersip in 2000 with all the correct fittings, labels etc - a nice conversion. When I attach a guage to the low side the compressor starts up, the pressure quickly rises to approx 45lbs and what I presume is a high pressure cut off stops the compressor, the system pressure then quickly drops and the compressor restarts. the whole cycle only takes about 15 seconds or so... I assumed that slow leakage over time had occured so began by adding a small amount of a combination of 2oz of oil and 2 oz of 134a...I saw no difference in the pressure fluctuations nor the cycle times so shut down the system. Before going further, I'd really appreciate some advice...There are two valves (needle valves) on both sides of the compressor but they don't look closed. Advice please????
I just had the good fortune of buying a 1988 F250 Diesel (IH 7.3 non turbo) from an older couple - few miles, always garaged and always dealer serviced. It hasnt been driven muvch in the last few years and has only 67K miles.
The air conditioner isnt blowing cold. It was converted to 134a by the dealersip in 2000 with all the correct fittings, labels etc - a nice conversion. When I attach a guage to the low side the compressor starts up, the pressure quickly rises to approx 45lbs and what I presume is a high pressure cut off stops the compressor, the system pressure then quickly drops and the compressor restarts. the whole cycle only takes about 15 seconds or so... I assumed that slow leakage over time had occured so began by adding a small amount of a combination of 2oz of oil and 2 oz of 134a...I saw no difference in the pressure fluctuations nor the cycle times so shut down the system. Before going further, I'd really appreciate some advice...There are two valves (needle valves) on both sides of the compressor but they don't look closed. Advice please????
Senior User
Joined: Sep 2003
Posts: 394
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Have it serviced by an AC mechanic. You know just enough to be dangerous. AC systems operate under high pressures when operating properly. Connecting the wrong things to the wrong port can cause an explosion with tragic consequences.
Please get adequate education about automotive AC systems before attempting to service one yourself.
Google Auto AC servicing techniques might help.
Please get adequate education about automotive AC systems before attempting to service one yourself.
Google Auto AC servicing techniques might help.
Posting Guru
Joined: Jan 2002
Posts: 1,346
Likes: 8
From: Baltimore
Your symptom indicates the system is low in refrigerant due to a leak in the system.
The low pressure cycling switch mounted on the accumulator is what controls the
compressor clutch engagement.
You didn't mention what the high high side pressure was?
There is no high pressure cut off switch. There is a high pressure relief valve
on the compressure hose manifold which vents excessive high pressure to the atmosphere and then the relief valve closes.
Remove the electrical connector from the low pressure cycling switch that is mounted
on the accumulator. With the connector removed, jump the two wires on the connector
together. Start the vehicle and turn on the AC. The compressor clutch will stay
engaged. If the system doesn't cool, you're most likely low on refrigerant.
Don't run the system this way very long because if you're low on refrigerant,
the oil that lubricates the compressor is not being circulated.
The two service valves on the compressor are used to isolate the compressor so
the compressor can be changed without discharging all of the refrigerant.
The low pressure cycling switch mounted on the accumulator is what controls the
compressor clutch engagement.
You didn't mention what the high high side pressure was?
There is no high pressure cut off switch. There is a high pressure relief valve
on the compressure hose manifold which vents excessive high pressure to the atmosphere and then the relief valve closes.
Remove the electrical connector from the low pressure cycling switch that is mounted
on the accumulator. With the connector removed, jump the two wires on the connector
together. Start the vehicle and turn on the AC. The compressor clutch will stay
engaged. If the system doesn't cool, you're most likely low on refrigerant.
Don't run the system this way very long because if you're low on refrigerant,
the oil that lubricates the compressor is not being circulated.
The two service valves on the compressor are used to isolate the compressor so
the compressor can be changed without discharging all of the refrigerant.
Thread Starter
|
New User
Joined: Jul 2010
Posts: 4
Likes: 1
Thank you!
Your symptom indicates the system is low in refrigerant due to a leak in the system.
The low pressure cycling switch mounted on the accumulator is what controls the
compressor clutch engagement.
You didn't mention what the high high side pressure was?
There is no high pressure cut off switch. There is a high pressure relief valve
on the compressure hose manifold which vents excessive high pressure to the atmosphere and then the relief valve close
Remove the electrical connector from the low pressure cycling switch that is mounted
on the accumulator. With the connector removed, jump the two wires on the connector
together. Start the vehicle and turn on the AC. The compressor clutch will stay
engaged. If the system doesn't cool, you're most likely low on refrigerant.
Don't run the system this way very long because if you're low on refrigerant,
the oil that lubricates the compressor is not being circulated.
The two service valves on the compressor are used to isolate the compressor so
the compressor can be changed without discharging all of the refrigerant.
The low pressure cycling switch mounted on the accumulator is what controls the
compressor clutch engagement.
You didn't mention what the high high side pressure was?
There is no high pressure cut off switch. There is a high pressure relief valve
on the compressure hose manifold which vents excessive high pressure to the atmosphere and then the relief valve close
Remove the electrical connector from the low pressure cycling switch that is mounted
on the accumulator. With the connector removed, jump the two wires on the connector
together. Start the vehicle and turn on the AC. The compressor clutch will stay
engaged. If the system doesn't cool, you're most likely low on refrigerant.
Don't run the system this way very long because if you're low on refrigerant,
the oil that lubricates the compressor is not being circulated.
The two service valves on the compressor are used to isolate the compressor so
the compressor can be changed without discharging all of the refrigerant.
Thank you for the helpful reply. I, in fact have substantial AC design and installation experience in marine and industrial systems. I doubt theres anything seriously amiss here other than accumulated loss of refrigerant but as Im not familiar with this installation and have no manuals elected to stop as soon as I observed something unexpected. I was disappointed there was no bullseye (which clues you into my age). I appreciate your very helpful and relevant information. Again Thanks
