I have a 99 F-150 and occasionally the heater quits blowing air. The fan is still running fine. When this happens, there is no air blowing anywhere. After a while it starts working again. Is there a flap that is closing somewhere? I plan on looking at it this weekend and wanted some input before starting. Thanks.

 

When it does it again, see if there is air coming out of the defroster vents. If so, you have a vacumm leak some where.
-Matt

 

there is a door that send the air to the defroster or the floor as nascar said. it is vacuum controlled. if you loose vacuum, the fail safe mode is to direct the air to the defroster to keep the window clean. vacuum is supplied by a 3/16 diameter plastic tube, behind the battery that goes thru the firewall toward the glove box area. only tube going thru the wall in that area. it goes to the back of the center **** that selects "defroster, panel, floor".

 

When it happens, I don't get air anywhere. I just came in after looking at it and of course everything is working fine now.

 

Have any unruly passenger's feet lately (possibly kicked or nudged)? Or posibbly have
a sheet of paper/plastic grocery bag lodged in the blend door? Maybe check that.
Rob

 

I checked operation of two doors. One is left of the hump and I can watch the operation of the lever. The other is directly above the fan motor and opens and closes when moving the control ****. Everything works fine at the moment,but when it quits again, I know what position they should be in. Are there only two doors? Thanks for the idea, though.

 

by any chance did you suck something into it? i had a customer come in and we chased this issue for 3 hours. it turned aout to be a small plastic bag go sucked up into it and would block flow every so often.