No heat sometimes and got heat sometimes

Hi,

If there is a heater control valve, it will be vacuum operated and on the inlet side hose under the hood. Chances are it doesn't have one. When one hose is hot and the other warm, do you get any heat? Have you tried flushing the heater core and back flushing it?

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Here are directions for the procedure. I would try this to see if it helps.

1997 Ford Truck F 250 2WD HD Pickup V8-351 5.8L VIN H EFI
Back Flushing-Heater Core
Vehicle Heating and Air Conditioning Heater Core Service and Repair Procedures Back Flushing-Heater Core
BACK FLUSHING-HEATER CORE
All engine cooling system flushing and back-flushing procedures must include a separate back-flushing of the heater or air conditioning/heater system heater core, after the flushing or back-flushing of the engine cooling system. This will prevent engine cooling system particles from clogging the heater core tubes and reducing (or eliminating) coolant flow through the heater core.

The heater core must be back-flushed separately from the engine cooling system for proper back-flush water flow direction through the heater core.

1. The correct heater core back-flushing procedure is as follows:

Disconnect the outlet heater water hose from the water pump fitting and install a female garden hose-end fitting adapter in the end of the outlet heater water hose. Secure with a hose clamp.

2. Connect the female garden hose-end of the outlet hose clamp to the male end of a water supply garden hose.
3. Disconnect the heater core inlet hose clamp from the engine block fitting and allow to drain onto suitable container.
4. If a heater water control valve is installed in the heater core inlet hose clamp, check to be certain the heater water control valve is open (no vacuum).
5. Turn the water supply valve on and off several times so that the surge action will help to dislodge larger stubborn particles from the tubes. Allow full water pressure to flow for approximately five minutes.
6. If a heater water control valve is installed in the heater core inlet hose clamp, apply vacuum to the water valve vacuum motor to make sure heater water control valve operates and closes properly to prevent water leakage. Replace the heater water control valve if required.
7. Remove the heater water hose and female garden hose-end adapter from the end of the outlet hose clamp and connect the outlet hose clamp onto the water pump fitting.
8. Connect the inlet heater hose onto the engine block fitting.
9. Fill the cooling system.
10. Test the system for proper heater performance.

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Let me know.

Joe

Hi, Ray. If it works when you flush it and then stops plus one hose is hot and the other isn't, something is causing it to block. When you say you flushed it with purple power, do you mean the degreaser or did you use a flush product? Did you take note if there is a heater control valve on the supply side to the heater core?

Joe