interesting AC issue
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Fleet Mechanic
Joined: Nov 2005
Posts: 1,508
Likes: 87
From: North Carolina, Raleigh
Last summer, depressurize the system, unbolt, vaseline on new orings, recharge it. Be very careful with the low pressure sensor, which screws in the accumulator. I cracked the sensor, ford has a replacement that requires a new pigtail...this sensor IMO doesn't work with the 7.3L...I've tried 2! My compressor turns on even when the switch in the cab is not on AC or AC max, been trying to find a 7.3 with the original sensor and pigtail that I can salvage. But overall the job is very easy.
roger that ,, thanks
More Turbo
Joined: May 2016
Posts: 717
Likes: 9
Just some suggestions and a couple questions:
Q: What was the ambient Temperature?
Q: What was the Static Pressure before starting the Compressor? Both should be equal. And, R134a pressure should be near ambient temperature. As such, this is "general" indication of the system being charged.
Q: What was the low side pressure? If it was low, with little or no fluctuation, or, is very slow to recover based on a Pressure Temperature Chart, you're looking at a blockage. We know the high-side pressure is well above 275 psig so we can "assume" based on this there is an issue. But where? The low side will tell the tale. Otherwise, the compressor itself may have a blockage within.
Most often, these three observations will get you moving in the right direction.
I would evacuate the system, and remove Orifice Tube for inspection. If there is any debris, its a sign of something has come apart. Specifically, the compressor.
Now, if you have debris that has blocked the Orifice Tube, the system lines will need flushing. You will want to replace (dependent upon what materials are identified) The Orifice Tube, Condenser, and Accumulator. And, if there is metals, the Compressor.
Why?
The Tube can not be cleaned if debris has blocked it. Blowing air through it will expand the screen openings and make them inconsistent.
The Accumulator is basically a holder for desiccant which traps moisture and impurities.
The Condenser is a stack-plate cooler. Because of its design, they are virtually impossible to clean or flush.
If you don't replace these parts you may have A/C for a week, month, or year. But, some certainty that it will fail again.
As for the Compressor, we are blessed, in that, ours are relatively inexpensive compared to most.
If you're doing the work yourself, or you take it somewhere if you have changed the parts:
Don't let the system open for more than 24 hours.
Make certain they know to add PAG Oil and describe in detail what parts were changed.
This is also an excellent time to add Dye. Then, should a leak occur, its much easier to identify with a UV Light than a "Sniffer".
Q: What was the ambient Temperature?
Q: What was the Static Pressure before starting the Compressor? Both should be equal. And, R134a pressure should be near ambient temperature. As such, this is "general" indication of the system being charged.
Q: What was the low side pressure? If it was low, with little or no fluctuation, or, is very slow to recover based on a Pressure Temperature Chart, you're looking at a blockage. We know the high-side pressure is well above 275 psig so we can "assume" based on this there is an issue. But where? The low side will tell the tale. Otherwise, the compressor itself may have a blockage within.
Most often, these three observations will get you moving in the right direction.
I would evacuate the system, and remove Orifice Tube for inspection. If there is any debris, its a sign of something has come apart. Specifically, the compressor.
Now, if you have debris that has blocked the Orifice Tube, the system lines will need flushing. You will want to replace (dependent upon what materials are identified) The Orifice Tube, Condenser, and Accumulator. And, if there is metals, the Compressor.
Why?
The Tube can not be cleaned if debris has blocked it. Blowing air through it will expand the screen openings and make them inconsistent.
The Accumulator is basically a holder for desiccant which traps moisture and impurities.
The Condenser is a stack-plate cooler. Because of its design, they are virtually impossible to clean or flush.
If you don't replace these parts you may have A/C for a week, month, or year. But, some certainty that it will fail again.
As for the Compressor, we are blessed, in that, ours are relatively inexpensive compared to most.
If you're doing the work yourself, or you take it somewhere if you have changed the parts:
Don't let the system open for more than 24 hours.
Make certain they know to add PAG Oil and describe in detail what parts were changed.
This is also an excellent time to add Dye. Then, should a leak occur, its much easier to identify with a UV Light than a "Sniffer".
Papa Smurf
Joined: Nov 2009
Posts: 1,080
Likes: 204
From: Woodstock, GA
When I had intermittent cycles I found the pigtail coming off compressor was making a faulty connection. You could wiggle the wires...and compressor would come on. Had this happen numerous times over 20 years with a 7.3. Guessing I layed on that connector when working on truck a lot..... 
Hotshot
Joined: Mar 2014
Posts: 10,750
Likes: 1,065
From: Douglassville, PA
Last summer, depressurize the system, unbolt, vaseline on new orings, recharge it. Be very careful with the low pressure sensor, which screws in the accumulator. I cracked the sensor, ford has a replacement that requires a new pigtail...this sensor IMO doesn't work with the 7.3L...I've tried 2! My compressor turns on even when the switch in the cab is not on AC or AC max, been trying to find a 7.3 with the original sensor and pigtail that I can salvage. But overall the job is very easy.
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