1978 F150 output temperature variation
Posted: Wed Sep 16, 2026 7:56 pm
Good evening. My name is Eddie. I’m working on my 1978 F150 AC. I installed a new Classic Auto Air unit in my truck about a year ago. The temperature at my center vent varies 15 to 20 degrees as I’m driving on these hot days. My temperature goes down to 37 and up to 57 over and over. I just fixed a leaking condenser line and recharged it a week ago. I vacuumed the unit down and put 24 ounces of R134 into it. The guages read 35-40 low side and 275 high side with ambient temperature around 90 degrees. The system cools good but climbs to 55-60 degrees while the compressor is off. I’ve checked my water valve. Bypassed the heater hoses. I lifted the thermostat tube about an inch from inside the case. Monitored my engine water temperature. I’ve contacted the tech support at CAA for advice.
This is a OEM truck with no bell or whistles. The only thing that’s not stock is the CAA air conditioner unit. It has performed this way since day one of use.
I will gladly consider any ideas that would clear this up for me. Thanks in advance for the advice.
This is a OEM truck with no bell or whistles. The only thing that’s not stock is the CAA air conditioner unit. It has performed this way since day one of use.
I will gladly consider any ideas that would clear this up for me. Thanks in advance for the advice.