OT - 1997 F-150 heater problem

1997 F-150 engine temp is normal, heat is in the ducts, fan is blowing normal on all speeds, warm air is not blowing out of ducts. I can feel warm right at the vent, but it is not blowing out. It is doing this in all settings, defrost, panel, and floor. Engine is running fine the entire time, doesn't sound or feel like a vacuum leak. I suspect a blender door or vacuum control module, possible partial blocked fan. This doesn't happen all the time, sometimes starts out working fine then stops. Has anyone had a similar experience to guide me? I hoping I don't have to pull the whole dash apart?

I had a Chevy 3/4 ton that had the same problem. Engine was hot, but no heat. It had been used by a contractor. I called the Chevy shop and they said to check for something blocking that door. I could reach in there and I found a hand full of pencils and pens. Worked fine after that. Hal

Wonder if that's what's wrong with my 85 Ford F250. AC blows out the defrost and floor vents but not out the dash vents where it should.

Vac leak or low vacuum to control switch< lots of supply line leaks > ,bad control switch < replaced lots of them > Or possibly vac operated door motor bad . If you have access to a shop with a "smoke Machine " very easy to find . If no smoke machine ,I made a homemade smoke checker yrs ago ,worked great . I can give you idea how to make it if you need .

i had this problem once , check your anti freeze

Fire away,email's open. Thanks.

Well the idea behind this is to inject smoke into vacuum lines,but can be used to find leaks in any contained area. oil leaks , exhaust etc .
I used a cheap cylinder leakage tester to control air pressure but any way you have of regulating air pressure down to 1-2 lbs will work . I took brass fittin gwith nipple , this nipple would be hooked into vac line to be tested. other end of nipple was drilled out so a small cigar would fit into it , this nipple would then be put in end of heater hose about 6 inches long . other end of heater hose was hooked to outlet of regulator . Light cigar, get it going good , put end in nipple , put nipple in heater hose with lite end towards incoming air . trun reg till you get smoke out end of nipple to be connected to vac line . It doesn;t take much air , too much and you'll vaporize cigar to fast . I used this for many years until I bought a smoke machine . It works great , lot of people warned about fire hazzard , but I was carefull with it's use . Don;t used on or around fuel leaks . Make sure engine is off when using it . After few minutes of smoke injection , check all vac lines with flash light . look under dash engine compartment ,etc. You'll be amazed at what you can find . Rough running or lean engine ? Hook into vac line going to intake manifold, smoke away ! Bad ,leaking Egr valves, pull offs , brake boosters , cruise control servos , you name it, if it 's leaking ,you'll find it .
Wish i had a pic of it , explains it lot better . I 'll see if I can dig one up .

Your heater core could be full of dust and dirt, but it sounds like the problem I was having. Does your truck take a longer than usual time to warm up? Might need a new thermostat. It could have a piece of paper or something in the intake to the heater as well. Dave