low on coolant the heat will often act up. it might work for a while then stop for a while. or not at all.

also if the car has been overheated recently sometimes the crap is loostened and deposited in the heater core and plugs it up.

and of course it could be the valve that diverts the water flow to the heater.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.