Hi,

Last summer, my compressor started siezing up on my 83 300D. Replaced it with a rebuilt one and had a professional retrofit done, where they solvent flushed the system, replaced the o-rings, dryer, etc., and then filled it with ester oil and r134a. Worked great, no issues, cold air.

Last monday, I was driving along and it was particularly hot. Not summer heat, which I know the system CAN provide cold air in after the retrofit, but about 85 and sunny.

All of a sudden, while driving on the highway, the air went warm. I just rolled down the windows and thought maybe the system wasnt keeping up, or it was because I had moved the dial from about 16 to about 24C. I moved it back, and after about 5 minutes, the air went cold.

Later, I was in traffic, and it went warm again. Really warm, more like as if I had turned the heat to max. I drove home with the windows down, and to my dismay, when I popped the hood, the metal fittings on the cold side of the AC system were very cold and had condensation.

This morning I drove the car again. at the start it was cold, but then all of a sudden, as the engine got up to temp, it went hot again.

The aux fan comes on, BTW, signifying that the pressure switch is working. Sometimes I see the refrigerant bubbling in the sight glass, signifying that its working. the metal fittings condense water on them, and are quite cold. So what could it be?

I am thinking maybe the compressor is cycling less than it usually does. Not a good correlation to the fact that the aux fan is going on (low pressure should keep the fan and the compressor off), but its just what I notice.

Out of curiosity, Im thinking of adding some r134a. I need to be careful though, as the way I understand it, you can only put in 85% of the weight of refrigerant, since 134 runs at different pressures. So how would I do it? If I get an r134a gauge (which I have from one of those interdynamics kits), itll tell me the pressure that Im at, and have the ok range at 25-45psi. But how does that correlate to the correct amount of refrigerant, and the correct weight and pressure fill quantities that my system would need, since it should have the 85% of the amount of r12 required?

I drive the car all the time, so I really need it to be blowing cold. It cant be blowing heat that feels like max heat at me.
ACC seems to be working right, as do the vents. No issues with anything on the car at all.

What should I do? Any hints, tips or suggestions? anything would be appreciated.

Thanks for your time reading this long post.

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
2008 ML320 CDI (199k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)