The most common cause of this failure is a broken blend door. Check heatertreater.net for diagnostic information and an inexpensive fix.
The thermostat may be stuck open.
You are in the beginning throws of blend door failure. Check www.heatertreater.net for more information on diagnosing and fixing the problem.
check your thermostat, if that isn't it you might need a new heater core. had one put in my f150 for about $150. With my car, it was Heater matrix clogged with radiator sealant. The workshop cleaned it and it's start working fine!
Low coolant? Defective thermostat? Heat control cable not adjusted properly? Heater core plugged or airbound?
Burried behind the dash on the passenger side, good luck.
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Low on coolant. Thermostat stuck open. Heater core plugged up. Temp blend door malfunction.
The temperature blend door may not be hooked up or is not working. Check that the temperature can be changed in any mode of operation. It could be a disconnected or failed actuator also.
I don't know about the outside diameter of the hoses but, the outside diameter of the heater core inlet and outlet tubes are 3/4" (inlet) and 5/8" (outlet).
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How do I locate the heater blend door actuator in a Ford f150 pickup