Rear defrost.

[amc401]

Don’t have the book for this thing yet, and the interior is gutted. I see a switch on the dash that is for the rear defrost. The back window has no normal defrost lines going through it. But on closer inspection I see the outside rear slots above the window lead fresh air into the car. Also I see a hose that is about 1in or so in diameter going up the inside of each rear panel. Looking at the headliner I see the liner is vented. Are all these connected together? If so what is the switch for? Does it use a blower motor for the defrost?

[BQS4]

Originally Posted by amc401 Don’t have the book for this thing yet, and the interior is gutted. I see a switch on the dash that is for the rear defrost. The back window has no normal defrost lines going through it. But on closer inspection I see the outside rear slots above the window lead fresh air into the car. Also I see a hose that is about 1in or so in diameter going up the inside of each rear panel. Looking at the headliner I see the liner is vented. Are all these connected together? If so what is the switch for? Does it use a blower motor for the defrost?

The hoses you see are for drain. The vents above the back window are for air flow. The GT used a heating element in the back window. The switch for rear defrost is in all GTs as the switches were made that way. Then if the GT was ordered with rear defrost, the switch was already there. To be sure it was originally equipped with defrost, it would have the element in the back glass, and a red LED just below the driver's side dash vent.

[kwilford]

Originally Posted by amc401 Don’t have the book for this thing yet, and the interior is gutted. I see a switch on the dash that is for the rear defrost. The back window has no normal defrost lines going through it. But on closer inspection I see the outside rear slots above the window lead fresh air into the car. Also I see a hose that is about 1in or so in diameter going up the inside of each rear panel. Looking at the headliner I see the liner is vented. Are all these connected together? If so what is the switch for? Does it use a blower motor for the defrost?

A heated rear window using an electric grid was a factory option, but the switch was in place in either case. An aftermarket "stick on grid" can be bought and installed on the inside of the rear window, and then a relay hooked up with the appropriate wiring to make it function like the factory meant it. For details on how to wire it properly, just look at the electrical schematics from a Factory Service Manual (FSM).

The rear vents above the rear window actually draw air OUT from the car, as they sit in a low pressure area. I think that GM called it "Astro-Ventilation" or some such gimmicky name. But since the air exits along the sides of the rear window, the air flow does actually help clear the window when the car is moving.

The one inch hoses along the insides actually drain water from the vented area, and exit down on the rear floor pan, through a couple of funky rubber grommets typically called "duck-billed grommets" (the bottom of the grommets are pinched flat like a duck's bill), and have nothing to do with air flow.

HTH

[ging]

I have looked for a while for one of the stick-on defrosters and have had no luck. If anybody knows where one can be found I'd be interested in knowing. I think I'm right in believing that a new replacement window with a defroster is not available (?) and often the old ones you can find have broken elements or don't work altogether. Maybe I'm just being pessimistic... .
Ging

[kwilford]

Originally Posted by ging I have looked for a while for one of the stick-on defrosters and have had no luck. If anybody knows where one can be found I'd be interested in knowing. I think I'm right in believing that a new replacement window with a defroster is not available (?) and often the old ones you can find have broken elements or don't work altogether. Maybe I'm just being pessimistic... . Ging

I bought mine last year at the local NAPA. That said, I suspect that rear window defrosters are in bigger demand up here in the land of ice and snow than in Georgia and other tropical states

[BQS4]

Keith;
We may not get snow, unless it's up in the mountains, but, it does get cold enough to have frost which gets hard to scrape off, but, having a defroster does help. There are more sold down here than you might imagine.

[Dennis Texas]

Originally Posted by BQS4 it would have the element in the back glass, and a red LED just below the driver's side dash vent.

Removed my dash out of second 72 yesterday noticed that light (this is evidently the only real factory installed rear defroster car I own out of all of them) I thought it was a PO add on, actually I though it was an audio jack for the stereo someone had added until I took it out and saw it had a bulb. Thanks for the insight I was going to pitch it and not go back with it but since it has a purpose have to go find it now