Heater Issues
 

Car:
1989 Mustang LX 5.0L, AOD tranny

Scenario:
Heater is not working properly. If I use the lowest blowing setting possible it will push out some warm air, if I turn the blower up it pushes cool air

My thoughts:
I've already verified there is enough coolant in the radiator. The only thing I've noticed is the car appears to be running cooler than normal, in part due to the air intake I did last Saturday? Maybe that is just a coincidence. Anyway, the temperature guage sits at 5/8's, verses the 3/4 it normally sits on a warmer day.

Anyone know what else I can check? I don't mind the cooler temperature, but when I can't even defrost my windows I figure I need to do something.

Thank you.
Justin

Some possibilities:

Blocked heater core

Baffle control compromised: The heater is always on regardless of control settings (heater core is always being subjected to circulating coolant). However, there is a baffle which is controled by a bicycle type wire that connects to your hot/cold blend control knob. If the baffle isn't opening all the way, that would explain why you're only getting hot air at low fan speed settings. At high speeds, the cold air won't have enough time to heat up if the baffle is only partially open.

Thermostat to low

Leaking heater core is evident by windshield fogging up with a greasy (coolant) vapor.

Hey mpj76:
When I turn the knob for hot/cold I can feel the air get cooler or warmer. I can also "hear" the baffle opening or closing. But your idea that it's only partially opening sounds logical. What's a good way to test this or find/fix it?

The thermostat is something I'm going to look into. Maybe it's constantly open, not allowing the engine to fully warm up? Something else I noticed is it appears to be running cooler than normal.

If the heater core is blocked, is this an easy fix? Will it be found in a Chilton's manual?

Thanks again.
Justin

my guess is also that your baffle or damper that directs air from the fan through the heater coil is stuck. Try to remove the cable from the damper lever and check the damper's operation by manually moving the lever, then check the cable operation by rotating the temp knob, somewhere therein lies your problem, given your getting hot water to the coil.

yes,

Step 1: Remove dash
Step 2: replace core
Step 3: installation is opposite tear-down

it's about a 500 dollar job for a shop to do.