77 heater sorta working...?

[Trialsallday]

Hi guys, on a 77 heater box.. what is the purpose of the upper vents ? It seems only cold fresh air comes out of them. The new air comes in through the top right of the box and never gets a chance to pass threw a hot heater core because the core is under the vent so the air comes into the box and streight of the front upper vent ..
Some hot sore comes out of the bottom vent though because that air gets a chance to warm up since it passes through the core then out he bottom.
Kinda like having the AC and heat on at the same time ..
There is a little door that blocks the upper vent but it doesn’t seal up that good and plenty of cold air still comes out that way.
Needless to say my cab takes forever to warm up and never gets really warm...
Am I doing something wrong ?

 

[Pierps]

It might be time for a bit of maintenance on your heater unit. I've been away from the forum for a few years, so I'm not sure if Shane is still active. But I bought one of these kits a while back. I remember him also having a thread on how to do the rebuild. Shane's user name on this forum is AATLAS1X.

Heater Restoration Kits 40-45-55 Series

 

[GA Architect]

Hi guys, on a 77 heater box.. what is the purpose of the upper vents ? It seems only cold fresh air comes out of them. The new air comes in through the top right of the box and never gets a chance to pass threw a hot heater core because the core is under the vent so the air comes into the box and streight of the front upper vent ..
Some hot sore comes out of the bottom vent though because that air gets a chance to warm up since it passes through the core then out he bottom.
Kinda like having the AC and heat on at the same time ..
There is a little door that blocks the upper vent but it doesn’t seal up that good and plenty of cold air still comes out that way.
Needless to say my cab takes forever to warm up and never gets really warm...
Am I doing something wrong ?

View attachment 1588177

It doesn't appear you are doing anything wrong. If you are not already doing this, maybe to help heat the cab quicker, try pulling out the 'fan pull' one more time so it turns the front heater fan on high, as well as the rear heater fan on.

I tend to keep my heater box on the 'defrost' setting. Even on the low setting, that little sucker will cook my right ankle.

 

[thebigredrocker]

Are the water lines to your heater open and can you feel them get hot?

When you select heat or def you should shine a light in the “vent” louvers and see a plate blocking airflow.

Vent or fresh air mode

Heat mode forces all air across the heat exchanger

In heat mode floor heat should be present

Defrost mode. Heat to windshield only.

 

[thebigredrocker]

Picture of the mode selection lever in case yours is missing

 

[TheHardWay]

Great explanation, Rocker - thanks!

 

[ginmtb]

So basically the upper vent will never push out hot air. Just heater and defrost settings will pass heat. Sometimes it would sure be nice to have heat come out that upper vent instead of down at the floor. Yeah heat rises I get that...

 

[Varty Yo]

I can never get it to do anything in defrost mode haha. With that said i can get the cab of my 42 up to a balmy 24c when its -20 outside. You might want to check the valve on the firewall to make sure its wide open mine gets stuck so the warm pull just slides in and out i have to manually tape the valve open and closed when i transition winter to summer and summer to winter.