A coolish morning, the sun warmed cabin felt nice when I got in. But soon down the road, the chill started to come in. No problem, turn on the heater fan and it was already set to 74, a toasty place to be . . . nothing but cool air. I increased the temperature setting . . . nothing but cool air. Eventually I set it on "HI" and warmth returned. But soon as I lowered the temperature, it soon cooled off. Current hypothesis: Make sure radiator coolant level in overflow tank and radiator is OK. MiniVCI check for any codes or problems. Check 12V battery (still original but marginal batteries can cause all sorts of 'funnies') Check cabin heater coolant circuit for blown fuse Any other thoughts or suggestions? Bob Wilson
Is the fan operation normal in AC and non AC modes? It's common for resistors in the blower motor control to fail, commonly causing loss of certain speeds while leaving other speeds unaffected.
That is the coolant level issue. I got home about 4 hours ago so it should be cool enough but it is drizzling outside. The radar shows about 4-6 more hours so I'll go out later. I'm home, warm and dry . . . keep it that way. Bob Wilson
That's more plausible than most of other guesses so far. A related possibility is an open circuit in wiring to that sensor.
