It might not make much difference, but when I used to have cooling problems I would try running the heater wide open. If the temp dropped significantly, I knew I needed some more cooling. If it didn’t, I had a restriction in the cooling system like a sticking thermostat, etc. Not a fool proof trick, but useful sometimes. The first time I saw a heater used in the summer was in a friend‘s new 427 Cobra. It was an early model and didn’t have the dual cooling fans, which he added later. This was in Oklahoma, which get pretty hot in the summer, and feels even hotter with the humidity. There are probably better ways to trouble shoot cooling problems than this, but it just came back to me. I also had an early Econoline with the 177 inch motor that the heater barely worked in. Turning on the heater made no difference in temperature, so I checked the heater control valve. It was plugged. Replaced it and the heater worked… and it would drop the motor temp a couple degrees in hot weather.
