front defroster question

[gabegt90]

I noticed that when i'm driving up a hill heat comes out of the window defroster vents. Is this normal? or do you think one of the blend doors is stuck open? does that affect heater atc sensor or the heater it self? any info would be very helpful

[89GrandMarquis]

I noticed that when i'm driving up a hill heat

I'm keying off of your description, especially the driving up a hill.

My Ford Electrical & Vacuum Troubleshooting Manual says that when the system has no vacuum, it goes to defrost mode.

I'm guessing that you have a vacuum leak somewhere in your system, either between the manifold and the A/C - Heater system, or within the A/C - Heater system itself.

I'm guessing that when you are driving up a hill, the manifold vacuum drops enough where it no longer can overcome the amount of leaking air. The amount of air that passes through the long vacuum hoses to the A/C - Heater system is pretty small, so you may have been leaking for some time, but didn't know it.

Another possibility (and maybe the first one to check) is the A/C - Heater check valve, which my book shows mounted at the Vacuum Distribution Block (which is on the firewall on my 1989 GM, behind the upper manifold), or the A/C - Heater Vacuum Tank. The Vacuum tank should allow operation when the manifold vacuum drops below normal, but I would expect that the check valve/vacuum tank would not come into play unless your manifold vacuum was really low, like you are really getting your foot into it. So, if to climb the hill, you have your foot in it quite a bit, the check valve/vacuum tank could be the culprit.

I'd check on the check valve first, then go from there.

[boXman]

Did you plug that hose you pulled off under the dash?

[gadget73]

Leak at the thermal blower lockout, a bad check valve, bad coffee can, or a crack in one of the lines for the dash or can is probably the problem. Its definitely a vacuum leak somewhere though.

[gabegt90]

Did you plug that hose you pulled off under the dash?

No I pluged it back in god I hate climate control Great so it could affect heater output as well great

[boXman]

You can pull it off for heat, just have to plug it so you don't have a leak.

[gadget73]

The climate control system really isn't all that horrible. The non-automatic wont do the temperature shift crap if it leaks, but it will change the air door positions. It seems like a lot of bs involved but mostly not that much of it fails, usually the temperature sensor in the dash, the blower lockout, the can, or one of the lines connecting to one of the above breaks. I've replaced all of it on my car, and the climate control works great now. $28 for the can, the TBL hit the trashcan after it exploded 1 week after I installed it, and the $40 something for a new temperature sensor got it sorted nicely.

[85crownHPP]

I still pull the vacuum line lol... I wonder if theres an adjustable vacuum valve you can buy to manually give/take vacuum from the blend door... *idea pops into head*