Hey all,

In the last two weeks, my '98 has been acting funny regarding the HVAC system. In the last 9 years I've owned it, the airflow has only ever come out of the defroster and nothing else. I've always figured there was a leak in the system that wasn't worth investigating since in the winter the defroster is most important anyway.

But randomly, after driving the truck with the heat on two weeks ago, when I shut it off for a few hours and restarted it, the system would not blow heat on any setting. No matter on low, high, feet, defroster...nothing.

A few days go by without driving, and the next time the truck is started, the heat DOES work, on any setting and fan speed (of course when I set it to the floor and so on, it still comes out the defroster).

Then, just last night, the heat came and went. Any idea what this could be? I'm not sure if it's the blower motor, since I thought you usually lose fan speeds one at a time, but I could be totally wrong. Thanks for any thoughts!

 

'98 has a cable actuated heat blend door. It's still possible something broke and the door is flopping around (although not terribly likely). You can pull the glove box and watch the white arm move as you move the temp control. Listen for the door moving inside the HVAC box, and if you approach either stop kinda quickly you can likely hear the door "clunk" as it fully opens or closes.

If that all checks out I'd say your problem is the cooling system itself:
-low coolant level
-t-stat stuck open
-heater core clogged
-air in heater core (VERY common)

 

This is very helpful, thank you! I'll look up how to remove the glove box and go from there. Thanks so much!

 

Does the blower work when you aren't getting heat? It just blows cold air?

 

It's all or nothing. Either I turn the setting to defroster, floor, and so on, and choose the fan speed and it blows hot air.

Or, I choose those settings and nothing happens at all. But, when it does work, it always blows hot air.

 

Sounds like the blower motor is failing.

 

Yeah, if your blower just isn't blowing that's an entirely separate issue

 

Okay, good point. Hopefully not too expensive of a fix.

 

If it's truly your blower motor they're inexpensive. If you only have HIGH fan speed it's your blower motor resistor. Both are easy to replace.

 

True, it does not look expensive. I'll take some time to run through all of these things and report back what I find. Thanks!