Heater does not work replaced thermostat and hoses to and from the heater core

Tiny
JOHN6419
  • MEMBER
  • 1984 FORD F-150
  • 4.9L
  • 6 CYL
  • RWD
  • AUTOMATIC
  • 100,000 MILES
The heater is not working in my truck. I have replaced the thermostat, the hoses to and from the heater core are both hot. So I believe the heater core is working, and the coolant level is good. The blower fan works (only on highest setting) but still cold air only. Any thoughts?
I appreciate it.
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Sunday, December 18th, 2016 AT 8:59 AM

6 Replies

Tiny
CJ MEDEVAC
  • EXPERT
Are the heater hoses so warm/ hot that it is hard/ impossible to hang on to either?

If this just is not happening, maybe your heater core is stopped up (not allowing hot coolant flow through it)

If you will leave the heater core in place (where it is nearly impossible to get to)

leave its hoses connected to it.

Take its heater hoses loose out at the engine.

Now you have two hoses with a little flexibility that are connected to the heater core.

You are not crammed against the firewall with no room to flush.

Back flush time!

I like to "blast" into one hose and then "catch" in a vessel from the other

(then switch hoses-blast in the other, catch in the other)

It may take a few "musical hoses" trips to backwash the core.

The "catching" allows me to maybe see what the heck was stopping up the core. Normally chunks of rust or a massive amount of that "stop leak" glitter looking material.

This method will not work if there is some sort of control valve that is closed in one of the hoses. (In itself, it could be the reason for 'no flow' through the core.)

I made a picture the last time we flushed one, it is not a good picture, you may see the process as we flushed just one direction, before we switched to go the other direction.

Keep us posted

The Medic
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Sunday, December 18th, 2016 AT 10:10 AM
Tiny
CJ MEDEVAC
  • EXPERT
I was kind of forced to hurry up by the wife on my answering this morning. Maybe a door is not moving inside your HVAC unit?

As you move dials, does the air move from one opening to the other? Feet/ face/ middle/ etc?

The "high" only fan may be a Bad blower motor resistor.

Keep us posted, I may be able to find a diagram (maybe exploded view) of your HVAC unit if needed.

The Medic
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Sunday, December 18th, 2016 AT 10:17 AM
Tiny
JOHN6419
  • MEMBER
Thanks for your help. I'll try it and let you know.
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Sunday, December 18th, 2016 AT 12:17 PM
Tiny
JOHNNY G.JR
  • MEMBER
Go easy on hose pressure at first, usually a reverse flush is customary. I have done this method with a solution of muriatic acid followed by a quick flush with water, Great results on a 1992 Lincoln Town car.
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Sunday, December 18th, 2016 AT 1:21 PM
Tiny
SATURNTECH9
  • EXPERT
If both heater hoses going into the heater core are getting too hot to hold then I would be making sure your blend/temp door is moving and operating when changing the temp from cold to hot?
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Monday, December 19th, 2016 AT 7:35 PM
Tiny
JOHN6419
  • MEMBER
Replaced heater core and now heat is working fine. Thanks to all of you for your help.
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Tuesday, January 3rd, 2017 AT 11:31 AM

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