I guessing this is a vacuum problem, but I don't know where to start looking. The temps finally dropped here, enough to use the heater on the way home. While sitting at a stop light, the heater got colder and colder until it was downright chilly. Once I pulled through the light and the rpms picked up a little, the heat came back. I had the heat coming through the top panels, but I checked this on the floor and it's a problem there also. Once I got home, I sat in the driveway with it in drive, just like at a traffic light, and it got cold. So I stuck it in neutral and brought the rpms up a touch to see if that fixed it. Sure enough, it got warmer. That makes me think it's a vacuum problem with the temp control somewhere.

Another problem that may or may not be related is the vent for the drivers side defroster. Nothing comes out of that one vent, even with the rest of the system blasting.

Anyone here run into this before? Any ideas are greatly appreciated. I don't wanna start randomly taking the dash apart.

Thanks!

 

Forgot to mention, this problem is with the 97 F150, not the 99 Expy (or the motorcycle, ha!).

thanks.

 

As of this morning, there's no heat at all. Aaarrrgh!

 

I Have had the same thing happen to my truck recently. And i am curious if you found out what the problem was?

 

No. Like a ding dong I goofed off the entire thanksgiving holiday and forgot about the heater problem. I'll get to it monday I hope since we're supposed to get freezing rain and sleet here on wednesday.

I'm 99% sure it's a vacuum problem, I just need to trace it down. Under the right circumstances, I hear a slight whistling sound, but that could be my imagination now since I'm looking for it.

I'll post here when I find it so maybe it'll help you out. The HVAC portion of this board is dead. I thought about reposting it over in another section.

 

I'm embarrassed to say, it was due to not properly maintaining my truck. The coolant was low by almost a gallon. You'd think that would cause the temp gauge inside to read a little hot, but it didn't. There wasn't enough coolant to properly fill the heater coils. I added water to check it out, and that was indeed the problem. Then I flushed the system and added the proper coolant/water mix, the heater works great.

mnjpando - I hope your problem is just as easy, post back here if it worked.