Heater only blows hot (well, warm) on full speed of fan
Ford Escort 55D (van) X-reg. The heater only blows hot on fan position 3 (full speed), fan doesn't work on 1 or 2. Heater blows cold after restart unless temp. control is moved to cold then back to hot whilst ignition is on and fan set to pos. 3. Sometimes returns to cold and has to be 're-set' by turning temp. control to cold and back to hot again, sometimes several times before the sound of a flap closing is heard, after which hot air is emitted as desired. Temp. control works only on max (hot) or min (cold) pos, nothing in between.
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CHECK FOR LOW COOLANT,NOT ENOUGH COOLANT IN THE SYSTEM.IF COOLANT LEVEL OKAY.THERMOSTAT NEED CHANGING STUCK OPEN.IF THERMOSTAT BEEN REPLACED.CHECK BOTH BOTH RADIATOR HOSES AND HEATER CORES HOSES THEY ALL SHOULD BE VERY HOT.IF ALL HOSES HOT AND BOTH HEATER CORES HOSES GOING INTO FIREWALL IS HOT.HEATER DOOR NOT OPEN ALL THE WAY OR STUCK.IF ONE OF THE HEATER HOSES GOING INTO FIREWALL HOT AND OTHER HEATER HOSE COMING OUT OF FIREWALL NOT HOT.MORE LIKELY HEATER CORE PLUGGED NEED TO FLUSH OUT COOLING SYSTEM.FLUSH OUT COOLING SYSTEM IF NOT BEEN DONE IN A LONG WHILE.
The heater door is probably stuck in the full heat position. It could be a problem with the heater door motor or the controller - you'd have to check for both mechanical and electrical problems under the dashboard.
I'm not particularly familiar with that vehicle but all that I have seen also have a valve that opens and closes to allow or restrict the fluid flow to the heater core. It could be a problem if you haven't already eliminated it. The air defecting doors under the dash that direct air to the floor or to the defroster are also suspect.
The blower motor resistor is bad, when you have the fan on high the fan motor (or blower motor) gets full voltage. When you have the switch on any other setting it gets reduced voltage via the "Blower Motor Resistor". That part is usually fairly close to fan motor in the duct work and is held in place with a couple screws and has a plug in going to with several wires. Sometimes that plug in gets melted to the resistor and the plug (or pig tail) has to be replaced too. This should be a fairly simple fix depending on the location of the resistor. The parts should be less than $100.00