! The Blower Motor Resistor Assembly, which is located behind the glove box is the problem...See photo below...Replace the assembly...While connector is off inspect pins with a magnifying glass and a bright light for bent or loose pins.
go here to check it out yours may be slightly diffrent and the new part may be slightly diffrent but I was able to make mine work.
http://www.fixya.com/cars/t8131833-2008_envoy_denalis_heater
-Rich
The year, make and model info would help but generally the heater blower motor resister is located close by the heater blower motor.
The front expansion valve is clogged.
The blower may simply have burned out. If the blower is out then the heater probably still works.
fuse will be in fuse box. it will be labelled, either, heater fan or blower
If it's the front passenger side ,I would say your heater core is leaking .
Check at the blower motor itself. Have it turned on and tap the end of the blower motor with a hammer. I did this and found out that the blower motor was going out. The blower motor is on the top passenger side under the hood. Also check the wire connections. Make sure they are seated good. If this includes for the heater then I would say the blower motor is bad.
A bad heater blower motor resistor would effect one or more blower speeds other than high.
The relay on the heater/blower circuit on a Ford Escort MK6 is probably behind the glove compartment. There are two popular places that Ford puts its heater/blower relay switches. The other place would be next to the blower motor itself.
There is no heater matrix for the back air vents, only and evaporator for the A/C. My suburban always blowed cold until I added an extra rear heater matrix.
Blown fuse.
Is it the blower motor or is it the fans in the front?if its the fans they will come on at anytime to help cool engine down better.If its the blower motor for the interior heat and air you got a electrical problem. Is it the blower motor or is it the fans in the front?if its the fans they will come on at anytime to help cool engine down better.If its the blower motor for the interior heat and air you got a electrical problem. If it is the blower motor for your heater then it is definatly you blower resistor
Blown fuse? Bad blower motor? Bad blower motor resistor? Bad blower motor switch?