The high tomorrow is 5F here in St. Paul and the fan of my heating system only works intermittantly. It usually runs when I first start the car totally cold in the morning, but it shuts itself off after about 15 minutes even though the interior temperature is no where near the set point. After this, the fan won't come on for the rest of the day, except for very occasional and too brief moments.
I suspect the car thermostat is stuck open since the water temperature stays around 60-70C and I know the fan isn't supposed to come on until the water gets hot. However, the "high" setting on the heater fan is supposed to override this and the fan does work when the car is first started and very cold.
Another clue is that the fan worked okay until the outdoor temperature dropped below 25F as it did recently (and will stay for the next few months).
I'm going to have the coolant thermostat checked out soon, but I'm not convinced that this is the problem.
Any suggestions?
Thanks, Tom
PS: My first car, a 1961 Buick LeSabre, had chronic problems with the heater. I finally replaced the temperature control with a threaded pipe water valve in the heater hose and a toggle switch under the dash to control the fan. Kind of crude, but it was foolproof.