Truck Repair A/C issues...again

bristles

Member
Looking at an older truck with a/c issues. Blows warm air. Had pressures checked, 38 and 250 and its 79 outside and raining. Can only manage a 10 deg drop in temp from outside to inside. This thing was built to use R12 and converted to R134. Expansion valve has been changed because pressures were 5 to 10 and 350.
 

Dauntless

Well-Known Member
When my older trucks AC blowed warm air, I never checked any pressures, I put a can of freon in it. Problem solved.
 

r3gulator3

Friendly Neighborhood Former Technician
Staff member
Supporter
Looking at an older truck with a/c issues. Blows warm air. Had pressures checked, 38 and 250 and its 79 outside and raining. Can only manage a 10 deg drop in temp from outside to inside. This thing was built to use R12 and converted to R134. Expansion valve has been changed because pressures were 5 to 10 and 350.
Receiver dryer been changed? If you got 38 psi you should be blowing some cold air have you checked the blend door or, coolant shut off valve to the heater core? (Depending on vintage)
 

Dauntless

Well-Known Member
I'd put a can of freon in it. If that don't fix it, Put another can of freon in it. If it's blowin a little bit of cold, 1 can should do it.
 

r3gulator3

Friendly Neighborhood Former Technician
Staff member
Supporter
Sure way to hillbilly it, just feed it refrigerant and if that don’t work, it’s just not gonna.

Based on ambient temp and relative humidity it’s pressures are slightly high. But not abnormally so. This indicates either a blend air issue or a restriction. But since they have already changed the TXV that is likely not the cause.
 

bristles

Member
sorry its not low on freon. Put in 4 pounds minus 20 percent as recommended by the dealer. Both valves on heater hoses are shut off. Heater hoses stay cool enough to keep your bare hand on them with water temp at 180. Its an International 1995 vintage with a hummin Cummins. Running a viscous fan drive to keep it cool. Have not changed the dryer yet. I did find that the control cable for the temp was broken but didn't make any difference when move to off position by hand.
 

Dauntless

Well-Known Member
Did you replace the compressor when you changed the freon?

Has the A/C ever worked after the freon change?
 

bristles

Member
Yes. New Compressor designed for R134a, system flushed about 5 years ago. Its always worked well enough, even at the start of summer this year. Every thing just went down hill in the last month. I have replaced the compressor, dryer, condenser, and temp cable that was broke. Waiting to find out if it will work Monday morning.
 

Mike

Well-Known Member
Staff member
this is idle up in the shop.
My truck does not cool in this situation if the ambient temp is high. Never has. That said, mine is a hybrid (Glider).

When it is hot outside, I manually turn the fan on if I am idling for any length of time. Pressure just never gets high enough to turn the fan on itself.

With the fan manually turned on, air blows ice cold and going down the highway it blows ice cold.
 

r3gulator3

Friendly Neighborhood Former Technician
Staff member
Supporter
Yes. New Compressor designed for R134a, system flushed about 5 years ago. Its always worked well enough, even at the start of summer this year. Every thing just went down hill in the last month. I have replaced the compressor, dryer, condenser, and temp cable that was broke. Waiting to find out if it will work Monday morning.
If you have a stand up shop fan try pointing that at the condenser on high and see if increasing the air flow thru the cooling package helps. Maybe your viscous drive fan isn’t engaging enough to pull air across it.
 
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