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Q: 97 Ford E150. Heater Not Working on 1997 Ford E-150

Club Wagon with auxillary (rear) heat.
Heat not working. A/C is good
Tried removing the heater hoses. Then flushing out the heater cores. Water flows freely. There are no coolant leaks.
Engine runs normally with no issues. Temperature gage starts out cold and moves to normal halfway position as expected. Internet queries suggest the heater control valve but it does not appear to have one. Or at least I have been unable to locate it. Thanks for your time. Tom - Laurel MD
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Vehicle: 1997 - 1998 Ford E-150 Econoline 4.2L
1997 - 1998 Ford E-150 Econoline 4.6L
1997 - 1998 Ford E-150 Econoline 5.4L

Symptom: No temperature control in heat or AC modes. Vehicles built before 2/25/98.

System: Heater/AC

Codes: N/A

Problem: Broken blend door in the heater case.

Test & Fix: A complaint of poor or no cold air when the air conditioning is commanded or poor or no heat when heat is commanded maybe a broken heater blend door. First perform normal diagnostics by checking the air compressor and thermostat operation. If these operate normally, the probable cause is a broken heater blend door. To diagnose the heater blend door gain access to the wiring on the temperature control switch. With the key on, check for a minimum of 9.0 volts between the Red/Light Green and Red/White wires using a digital voltmeter. If sufficient voltage is present, backprobe the Yellow/Light Green wire and watch the voltage change, while rotating the knob. Voltage should be about 8.5 volts at the full cold position to about 1.5 volts at the full hot position. If the switch tests good, the blend door is probably broken. Ford has issued TSB 98-5-10 concerning this issue with a revised heater case and blend door available. A related document, TSB 98-5-10, is available.
Additional Information
Have you checked under the van? Mine has a set of what looks like shut-off valves under the driver side about half-way to the rear.
field mice made a nest in your air/ heater duct and has restricted the air flow.
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