[updated:LAST EDITED ON 11-Mar-02 AT 09:02 AM (EST)]1994 F150 4.9L 2x4 5 speed no A/C

Original sympton - no heat in cab. Replaced thermostat with a 192F (temp indicator now points to N/O range for the first time!) but still not warm/hot heat into cab. The fan works, and the source selector (vent, floor, off, mix, def) works, but the temp selector won't go fully into the red (heat) zone. Can force it, but backs off once you let go (air pressured ?). And still not enough heat even when held in red zone. No apparent leak in the heater core - I'm not losing coolant. The hoses running into and out of the heater core are HOT! I'm thinking something is wrong with the temp selector switch - but does anyone have a troubleshoot procedure for it ? And how to remove it from the dash area ?

 

>1994 F150 4.9L 2x4 5 speed no A/C
>
>Original sympton - no heat in cab. Replaced thermostat with
>a 192F (temp indicator now points to N/O range for the first
>time!) but still not warm/hot heat into cab. The fan works,
>and the source selector (vent, floor, off, mix, def) works,
>but the temp selector won't go fully into the red (heat)
>zone. Can force it, but backs off once you let go (air
>pressured ?). And still not enough heat even when held in
>red zone. No apparent leak in the heater core - I'm not
>losing coolant. The hoses running into and out of the
>heater core are HOT! I'm thinking something is wrong with
>the temp selector switch - but does anyone have a
>troubleshoot procedure for it ? And how to remove it from
>the dash area ?


The temp selector is CABLE operated. The cable operates a swing door to the plenum chamber to divert air either direct to the vents or thru the heater core. The door may be stuck in the cool position also. You're gonna have to open the heater box (from the inside, get out your trusty haynes or chilton manual for this) and troubleshoot.

Bets are the outer cable has departed from either the switching assembly or the heater box, in which case you can try and snap it back on and hope it holds, and try to adjust the cable for full swing of the door, or get a new cable from the dealer.

Like adjusting the throttle cable on a lawn mower to get all positions.



Larry

 

i agree with what larry said. if you have checked all those other things it has to be the cable. i have fixed this probelm on my 88 f250 and my 87 mustang. there is a flimsy tin "clip" that holds the cable in the right position to open and close the door on the heater box under the dash. the cable can "slip" past this clip a little over time from constant adjustment of the temperature slider. as i recall you can get at it thru the glove box and from under the dash. just get it set up properly and re-crimp the clip.

 

Problem Solved - after some minor disassembly of the lower dash, glovebox, and heater core cover, I was able to get my hand contorted enough to reach the door of the heat box/vent. The door swing was impeded by a 4" long wooden cylinder containing graphite, and a grinning purple dinosaur on it ! Dang that Barney ! If I've told the kids once, I've told them a thousand times - don't leave your pencils on the dash ! Thanks for all the technical advice folks ! Murphy and Barney at the same time, what a dastardly duo..

 

damn i was gonna suggest to look for the Barney pencil too. common problem with these trucks. i think there was a factory recall. that is very funny. LOL