Heater not working

MVANN74

MEMBER
1997 FORD F-150
5.4L
V8
4WD
AUTOMATIC
205,812 MILES

My truck has no heat. Blower motor works fine. I've flushed heater core, flushed and changed coolant, changed thermostat, checked blend door and actuator. They are in working order. Burped system. Still no heat. Heater core is not leaking or showing any signs of wear or breakage. All hoses are good. And yet I still have no heat. Please help.

Monday, October 25th, 2021 AT 2:57 PM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

Try this and let me know the results.

Turn the heat on high. Start the engine and allow it to reach operating temperature. Turn the engine off and feel both heater core hoses between the engine and heater core. Do this as close to the firewall as you can get.

Are both hoses hot? If they are, the problem is on the inside. If one is hot and not the other, then the issue is either the core or the piping between the engine and the heater core.

Here is a link you may find helpful as well:

https://www.2carpros.com/articles/car-heater-not-working

Also, take a look at pics 1 and 2 below. Is that the actuator you checked behind the floor duct panel? I ask because there are a few different actuators. Let me know how you checked it as well.

Take care and let me know what you find.

Joe

See pics below.

Images (Click to make bigger)

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Monday, October 25th, 2021 AT 8:30 PM

MVANN74

MEMBER
65 POSTS

Neither hose is hot. I disconnected both hoses from heater core stuck hose in overflow reservoir and coolant came out of both hoses that are connected to engine. Checked blend door and actuator both are work as they should. I put hose in heater core itself and back flushed. Some rust and other stuff came out then eventually clear water came through. I have no heater control valve on this model year f150. Still no heat. I even tried reversing hoses. Still no heat.

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Tuesday, October 26th, 2021 AT 6:34 AM

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Okay, if they are both cold, then we must have an air block. If coolant comes from each hose when disconnected, have you tried removing the return line to see if coolant will flow from it from the core?

Try this. With the engine cold, loosen the return line from the heater core. Start the engine and see if you can push air out of the heater core by slightly removing the return hose. Keep it off or loose until coolant comes out.

Keep in mind, the heater core is physically high in the vehicle. That is where air wants to go and sit. Try my suggestion to see if it makes a difference. If this doesn't work, you will likely need to vacuum fill the system.

Let me know.

Joe

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Tuesday, October 26th, 2021 AT 5:21 PM