Defroster Issue..

[85beast]

heres the rundown: my 85 Grand prix has heat but no defrosters. U can feel heat coming from the vents but theres still fog. Can someone help?

 

[dan2286]

Are you saying heats coming from the front vents or defroster vents?

 

[maddog20_20]

If there is warm/hot air coming out of your defrost vents and you still have steamed up windows, your heater core might be leaking.

 

[G-Body_Vet]

One other possibility is that your climate control is bad or the vacuum lines under the hood are bad/disconnected (especially if the engine has been swapped and someone didn't bother hooking them back up). There's a flap that gets actuated to switch from the vents to defrost. No vaccum or a bad control unit won't allow the flap to change positions. When you slide the switch to defrost do you hear anything happen?

 

[dan2286]

One other possibility is that your climate control is bad or the vacuum lines under the hood are bad/disconnected (especially if the engine has been swapped and someone didn't bother hooking them back up). There's a flap that gets actuated to switch from the vents to defrost. No vaccum or a bad control unit won't allow the flap to change positions. When you slide the switch to defrost do you hear anything happen?

I'm pretty sure the default mode is defrost in case there is leaking vacuum lines or any other bad parts so you can still see if the windows did get fogged up.

 

[G-Body_Vet]

I'm pretty sure the default mode is defrost in case there is leaking vacuum lines or any other bad parts so you can still see if the windows did get fogged up.

I had an '80 Regal that would stick closed. It finally acted right after I persuaded the flap with a screw driver a few times. Nothing is out of the question when it comes to cars. :lol:

 

[madmaxstyle]

I had an 80 Chevy, I recently changed to motor and forgot to plug the vacuum line under the hood back in and (on top of a vacuum leak) the heater was stuck on vents (not defrost) It was easy in my case to figure out because the only thing I did recently was the drive line transplant and I figured it HAD to be under the hood.

Could be the control lever malfunctioned as well, can't rule anything out on a classic car. Generally you feel something wrong in that case though(ie Zero resistance). Also the vacuum lines goto little canisters or plungers that move in and out to pull open or close flaps according to the setting you put it on, one of those doors could be sticky or hard to open. (If your down there look to see if the doors are even physically connected) IIRC Theres only 2-3 flappy thingys under the dash, just follow the vacuum lines to the vacuum canister/plunger thingys. They look similar to the little ones you'd find on the carb.

No Vacuum means no heater controls other than fan high fan low, cold air or hot. In my chebby truck the default location was the vents not defrost. It would go back to vents if you unhooked the vacuum line.

 

[85beast]

Nope, all the vaccuum lines are hooked up, again the climate control works when you switch it and you can hear a hissing sound when its switched, but its brief. other than that the heater kicks. Not seeing any leaks from the heater core. im thinking its that door from the defrosters..

 

[83hurst-olds]

So, does it engage the air conditioning compressor? Most of them, with the defog setting chosen will run the location to the top of the dash and some to the floor. It will also engage the air conditioner compressor to dry the air before blowing it in, this will result in warm dry air.

 

[Blake442]

Something must be abstructing the diverter inside your heater box.

If there is no vacuum, the door goes to the default setting and you will get air out of both the defroster vents and the floor.
It is set-up this way as a safety precaution.