HVAC system - heater not blowing very hot

[patman0911]

My heater temperature output seems to have been dropping off lately. I started noticing it last year but it's really down this year. There is still warm air coming out of it so I'm getting some heat from it but not the scalding hot air I used to get from it - I used to be able to turn the car into a sauna. Now it's just lukewarm to slightly warm air coming out. This problem preceded my intake swap and didn't change one way or the other after the swap. I thought I flushed the core but I may not have flushed it in both directions.

Is there a valve that directs the flow of coolant through the heater core or is coolant always flowing through there? My repair manual is unclear on this.

Other possible causes would seem to be:

• Heater core is clogged and not enough volume of fresh coolant is flowing through it to keep it hot
• Heater core is blocked with leaves and pine needles and not enough air is flowing through it
• Air bubbles in heater core (seems unlikely as it should've worked it's way out sometime in the last 2+ years)
• Flapper valve in ducts is not moving all the way to full heat position and so ambient air is mixing with hot air
• ???
• profit!

Any other places to check for low heat output temperature?


The system doesn't seem to move as much air as it used to either, both A/C and heat so I guess I need to check that out too. The fan does operate at all 4 speeds. Probably a bunch of birds nest under the cowl

 

[wmburns]

Assuming the car is actually warming up to full operating temperature, my vote is #4.

OBTW, Mustangs do not have ANY valves in the heater lines. The full coolant flows through the core at all times. Heat is adjusted by a mixing damper under the dash. When the dash temperature knob is rotated, what is actually being done is the damper is being adjusted.

Because full coolant flows through the heater core at all times, that is why sometimes the heater cores leak. Hence the reason Ford added a flow restricter oriface in the heater hose.

Also, the coolant flow design needs the bypass flow of the heater to work correctly. That is why if the heater core is ever bypassed, the hoses should be LOOPED and not capped.

Suggest also checking the fan speed as this could cause low heat output. Check the fan speed resistor as it is bad about rusting out.

If the AC works fine, then focus on the damper. If air flow is reduced in heat and AC, focus on the fan and the air supply under the cowl.

Note. Should this be a damper, I am sure you will not like the fix. Getting access to the entire environmental box requires removal of the dash. While not positive, you may be able to access the blender control lines by removing much of the center console.

OBTW2; how cold is it where your are?

Good luck.

 

[patman0911]

Thanks for the info. I didn't think there was a valve in the coolant lines but the wording was mysteriously vague in the book.

Not looking forward to pulling the dash if it comes down to that.

I thought the A/C was not as cold as it used to be this summer, but it's still usable - I initially attributed it to the car being almost 14 years old and probably down on refrigerant a bit but perhaps it's related to the heating issues. I don't think the fan blows as hard as it used to either.

It's been in the 20s for the last couple of weeks but yesterday it finally started warming up some and we're up in the 50s today.