Replaced cycling switch. What temp do you have at the vent?
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From: Florida
I don't believe that they cycle on and off while they are above the set temp of the cutout switch. I could be wrong, but mine will run continuously and not cycle at all on a hot day (most summer days here). The new ones will, I think, but these shouldn't. I believe that freezing can be cause by a dirty and clogged evaporator coil, inside the car. It is a common problem especially if you live within 50 feet of a pine tree. the needles get in through the cowling in front of the windshield. Ask me how I know...Mark Edit: Check this thread:
https://www.dieseltruckresource.com/...t-t298318.html
https://www.dieseltruckresource.com/...t-t298318.html
Thanks, I did that already. Mine is clean 😁
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From: Phoenix AZ
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From: OK
From my experience IF your system has the right amount of refrigerant the pressure should be around 35 on the low side. ( keep in mind I’m going from memory) When the low side pressure starts getting where it runs higher...say 50’s it from my experience means the compressor is getting weak. I cant possibly see how the compressor wouldn’t be weak given the age...but I could be wrong. ( I hope I am!)
another thing...the ambient temp ( and humidity) where you live has a lot to do with things. I lived in OK and at idle I would get 39 degrees at idle! A shop put 134a with out asking! I took the truck to two different shops trying to get the truck to “COOL.” The coolest it has ever gotten since is 49 degrees! I’ve tried everything I know...134a is not the right refrigerant for these trucks.
Good of luck and hope my journey might help you!
another thing...the ambient temp ( and humidity) where you live has a lot to do with things. I lived in OK and at idle I would get 39 degrees at idle! A shop put 134a with out asking! I took the truck to two different shops trying to get the truck to “COOL.” The coolest it has ever gotten since is 49 degrees! I’ve tried everything I know...134a is not the right refrigerant for these trucks.
Good of luck and hope my journey might help you!
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Joined: Jul 2009
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From: Phoenix AZ
From my experience IF your system has the right amount of refrigerant the pressure should be around 35 on the low side. ( keep in mind I’m going from memory) When the low side pressure starts getting where it runs higher...say 50’s it from my experience means the compressor is getting weak. I cant possibly see how the compressor wouldn’t be weak given the age...but I could be wrong. ( I hope I am!)
another thing...the ambient temp ( and humidity) where you live has a lot to do with things. I lived in OK and at idle I would get 39 degrees at idle! A shop put 134a with out asking! I took the truck to two different shops trying to get the truck to “COOL.” The coolest it has ever gotten since is 49 degrees! I’ve tried everything I know...134a is not the right refrigerant for these trucks.
Good of luck and hope my journey might help you!
another thing...the ambient temp ( and humidity) where you live has a lot to do with things. I lived in OK and at idle I would get 39 degrees at idle! A shop put 134a with out asking! I took the truck to two different shops trying to get the truck to “COOL.” The coolest it has ever gotten since is 49 degrees! I’ve tried everything I know...134a is not the right refrigerant for these trucks.
Good of luck and hope my journey might help you!
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From: OK
Yes I’m sure you’re probably right. The only caveat is in OK the humidity is brutal....and that is probably a big factor. I tried pulling the cycle switch totally and it froze up with in minutes! (I got this idea I believe from Jim Lane) Who knows...I just wish it cooled good! 
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From: Phoenix AZ
Yes I’m sure you’re probably right. The only caveat is in OK the humidity is brutal....and that is probably a big factor. I tried pulling the cycle switch totally and it froze up with in minutes! (I got this idea I believe from Jim Lane) Who knows...I just wish it cooled good!
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I too live in AZ, 115 is a fun temp to survive in... I've got a 90 Ramcharger converted to a 91.5 IC 12v, I've installed all new components and originally ran R-134a and only got 50-60 at the vents on the best of days in the heat, regularly the system operated at very high pressures. I assumed the shop I brought it to over charged it. I also did some research and with R-12 being the refrigerant the system was designed for I was looking for something comparable in temp/pressure tables. It came down to a 90/10 propane butane mixture or 1,1 Difluoroethane (R-152a). I settled on R-152a as it's not as flammable as propane and seemed to match R-12 as close as I could get. Going with the system being designed to hold 44oz of R-12 I did the math and that came to roughly 26oz of R-152a. I evacuated and vacuumed the system, then charged with R-152a, and now 110-115 days I can pull 30-35 in the vent at 30mph! ohh and pressures are now 25 psi low and 250 high...
BTW - R-152a or 1,1 Difluoroethane is "Air Duster" commonly sold in the electronics section of any box store... Cost was $12 for 3 10oz cans.
BTW - R-152a or 1,1 Difluoroethane is "Air Duster" commonly sold in the electronics section of any box store... Cost was $12 for 3 10oz cans.
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From: Commerce, OK
I too live in AZ, 115 is a fun temp to survive in... I've got a 90 Ramcharger converted to a 91.5 IC 12v, I've installed all new components and originally ran R-134a and only got 50-60 at the vents on the best of days in the heat, regularly the system operated at very high pressures. I assumed the shop I brought it to over charged it. I also did some research and with R-12 being the refrigerant the system was designed for I was looking for something comparable in temp/pressure tables. It came down to a 90/10 propane butane mixture or 1,1 Difluoroethane (R-152a). I settled on R-152a as it's not as flammable as propane and seemed to match R-12 as close as I could get. Going with the system being designed to hold 44oz of R-12 I did the math and that came to roughly 26oz of R-152a. I evacuated and vacuumed the system, then charged with R-152a, and now 110-115 days I can pull 30-35 in the vent at 30mph! ohh and pressures are now 25 psi low and 250 high...
BTW - R-152a or 1,1 Difluoroethane is "Air Duster" commonly sold in the electronics section of any box store... Cost was $12 for 3 10oz cans.
BTW - R-152a or 1,1 Difluoroethane is "Air Duster" commonly sold in the electronics section of any box store... Cost was $12 for 3 10oz cans.
I converted to R-134a a couple years ago but I'm not happy with it. I'm looking to get a bigger condenser. AFAIK there is NO cycling switch on my 89. Just a low pressure switch which cycles sometimes. If I put in enough R-134a to make the low pressure NOT cycle it threatens to pop the overpressure valve on the compressor at around 600 psi on the high side. THAT'S a mess because the oil gets on the belt then and it squeels.
Edwin
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I guess that I got lucky or something,but I have a very stock '90, that I renewed the entire system, converted to R134A, Popped the over pressure valve, replaced it and have lived in ice cold air since. I would rather be lucky than good any day...Mark
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From: Tijeras, New Mexico, 7,000ft up
The present study investigates numerically the performances of an automotive air conditioning (A/C) system using R134a and R152a as working fluids for various engine running speeds. There are three engine rotation variations, i.e., 1000 rpm, 2000 rpm and 3000 rpm that represent idle, city and high speed conditions, respectively. The compressor volumetric efficiencies for 1000 rpm, 2000 rpm and 3000 rpm are 0.75, 0.65 and 0.55, respectively. The results show that the cooling capacities of R152a are slightly lower than that of R134a at the condensing temperatures of 40oC and 45oC. However, at the condensing temperature of 50oC, the cooling capacity of R152a is higher than that of R134a up to 5.0%. In addition, COPs of R152a are higher than that of R134a for all the condensing temperature. The increase of condensing temperature is more dominant to the COP improvement rather than the increase in engine rotation. The highest COP improvement is 13.5%.
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used a standard set of gauges with 1/4 line fittings and a side can punch tap. R-152a is compatible with PAG/Ester oils so if you're set up for R-134a your good to go unless you've lost oil...
there's conflicting studies on COP for R-152a vs R-134a, but I know that for the desert temps i'm living in, I've got a noticeably shorter period of time to cool the cab at 100+ degree temps with no cut out of cooling over long periods. Used to be that I had cool air halfway home from work after sitting all day, now it's comfortable in the cab by the time I hit the base gate and almost chilly by the time I get home. That's trying to cool a cab that regularly gets to 130+ degrees in the shade during this lovely time of year. My only ***** with the system now is the blower motor not pushing enough air... but I've got it maxed out (relay off high switch to a direct feed from the battery) and the motor is new, it's just the limits of the design.
there's conflicting studies on COP for R-152a vs R-134a, but I know that for the desert temps i'm living in, I've got a noticeably shorter period of time to cool the cab at 100+ degree temps with no cut out of cooling over long periods. Used to be that I had cool air halfway home from work after sitting all day, now it's comfortable in the cab by the time I hit the base gate and almost chilly by the time I get home. That's trying to cool a cab that regularly gets to 130+ degrees in the shade during this lovely time of year. My only ***** with the system now is the blower motor not pushing enough air... but I've got it maxed out (relay off high switch to a direct feed from the battery) and the motor is new, it's just the limits of the design.
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Joined: Jul 2009
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From: Phoenix AZ
used a standard set of gauges with 1/4 line fittings and a side can punch tap. R-152a is compatible with PAG/Ester oils so if you're set up for R-134a your good to go unless you've lost oil...
there's conflicting studies on COP for R-152a vs R-134a, but I know that for the desert temps i'm living in, I've got a noticeably shorter period of time to cool the cab at 100+ degree temps with no cut out of cooling over long periods. Used to be that I had cool air halfway home from work after sitting all day, now it's comfortable in the cab by the time I hit the base gate and almost chilly by the time I get home. That's trying to cool a cab that regularly gets to 130+ degrees in the shade during this lovely time of year. My only ***** with the system now is the blower motor not pushing enough air... but I've got it maxed out (relay off high switch to a direct feed from the battery) and the motor is new, it's just the limits of the design.
there's conflicting studies on COP for R-152a vs R-134a, but I know that for the desert temps i'm living in, I've got a noticeably shorter period of time to cool the cab at 100+ degree temps with no cut out of cooling over long periods. Used to be that I had cool air halfway home from work after sitting all day, now it's comfortable in the cab by the time I hit the base gate and almost chilly by the time I get home. That's trying to cool a cab that regularly gets to 130+ degrees in the shade during this lovely time of year. My only ***** with the system now is the blower motor not pushing enough air... but I've got it maxed out (relay off high switch to a direct feed from the battery) and the motor is new, it's just the limits of the design.
Administrator
Joined: Jul 2009
Posts: 5,311
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From: Phoenix AZ
The present study investigates numerically the performances of an automotive air conditioning (A/C) system using R134a and R152a as working fluids for various engine running speeds. There are three engine rotation variations, i.e., 1000 rpm, 2000 rpm and 3000 rpm that represent idle, city and high speed conditions, respectively. The compressor volumetric efficiencies for 1000 rpm, 2000 rpm and 3000 rpm are 0.75, 0.65 and 0.55, respectively. The results show that the cooling capacities of R152a are slightly lower than that of R134a at the condensing temperatures of 40oC and 45oC. However, at the condensing temperature of 50oC, the cooling capacity of R152a is higher than that of R134a up to 5.0%. In addition, COPs of R152a are higher than that of R134a for all the condensing temperature. The increase of condensing temperature is more dominant to the COP improvement rather than the increase in engine rotation. The highest COP improvement is 13.5%.
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The system was installed once I moved from SOCAL and needed AC, hasn't been under a tree since the install! But I have put in a boat access panel on the front of the suitcase and it's still clean and clear. I put new foam and duct taped the seams on the vents when it went back in the cab... I've got a finicky vacuum actuator that I have to give some love to though. I call it my weekend truck, drive it all week, and work on it all weekend...