I have a 1977 F250 with a 12-valve Cummins swap. During the swap I used a brand new Sanden SD7H15 compressor (New Sanden), cleaned the original evaporator (flushed multiple times) and clean exterior, new expansion valve, new hoses, new drier (universal), new universal parallel flow condenser. This was a while ago (2018ish). System developed a leak (I believe TXV) so I replaced it, along with a new drier. I also flushed the evaporator for good measure (AC flush chemical).
Pulled a vacuum for over an hour and let it hold. Held great so charged the system. Added approximately 50oz of R134a refrigerant to get the following pressures. The low side will not come up.
Currently:
Idle speed, truck stationary
Ambient: 80* F
Condenser inlet: 161* F
Condenser outlet: 80* F
High Side: 230-265 PSIG
Low Side: 15-17 PSIG
Vent: 32-33*F
Any thoughts? Cold and just leave it?
1977 F250 R134a Retrofit Low Side Low
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Powerstrokinit
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JohnHere
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Re: 1977 F250 R134a Retrofit Low Side Low
It sounds to me like the refrigerant charge is "off." What does the under-hood decal say about the amount of R-12 that should be in it? Does the evaporator freeze-up the way it is?
The system still might have a leak, and/or could have air and moisture in the system.
A system that holds vacuum is no guarantee that it will hold pressure, especially on the high side.
The engine must be running at around 1,800 RPM, not idle speed, for system testing to have any meaning.
The system still might have a leak, and/or could have air and moisture in the system.
A system that holds vacuum is no guarantee that it will hold pressure, especially on the high side.
The engine must be running at around 1,800 RPM, not idle speed, for system testing to have any meaning.
Member – MACS (Mobile Air Climate Systems Association)
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Powerstrokinit
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Re: 1977 F250 R134a Retrofit Low Side Low
JohnHere,
Thanks for the reply. I have no idea what the original system held as the decal is not there and the only thing left from the stock system would be the evaporator and I am not sure if it is a dealer installed or factory installed system. The evaporator is big though.
I did get some more numbers. With a lower charge, yes the evaporator was freezing up for sure. I don't think it is now.
Engine RPM: Idle
Ambient: 87*F
High Side: 320-350 PSIG
Low Side: 19-20 PSIG
Vent Temp: 34*F (Although I was driving it around earlier and it was at 40*F)
Condenser Inlet Temp: 182*F
Condenser Outlet Temp: 98*F
Thanks for the reply. I have no idea what the original system held as the decal is not there and the only thing left from the stock system would be the evaporator and I am not sure if it is a dealer installed or factory installed system. The evaporator is big though.
I did get some more numbers. With a lower charge, yes the evaporator was freezing up for sure. I don't think it is now.
Engine RPM: Idle
Ambient: 87*F
High Side: 320-350 PSIG
Low Side: 19-20 PSIG
Vent Temp: 34*F (Although I was driving it around earlier and it was at 40*F)
Condenser Inlet Temp: 182*F
Condenser Outlet Temp: 98*F