Chevy Astro and GMC Safari Forum banner

Rear Heat blowing cold

2K views 9 replies 5 participants last post by  Lumpy 
#1 ·
My current 2002 Astro is the first vehicle I've had with rear heat/air, so I am not familiar with it at all.

BACKGROUND: I've had many times the common problem with a key vacuum hose breaking preventing the air to be directed through the vents front and lower vents, defaulting to the defrost (windshield) setting. That particular vacuum hose comes from the engine block to a "T". Strangely, after replacing it the last time, when I turned on rear heat, the air coming through the vents stopped and defaulted to the defrost flow into the windshield. When I would turn off the rear heat, the air started coming back through the vents. When making the repair, I noticed that another short vacuum hose coming from the "T" and going to another "T" was in bad shape--sticky rubbery and collapsed on itself. So I replaced that, and when I turned on the rear heat, the front vent stayed blowing air like its supposed to and so was air coming from the rear heat vents near the floor.

PROBLEM: My joy was short lived when there was very hot air coming from the front vents, and cold air blowing through the rear heat/floor vents. I did notice that coming from the "T" where two new hoses were replaced was another vacuum hose that heads down and "disappears" which is in that same horrible, partially collapsed shape as the one described above. Could this be the culprit?
 
See less See more
#5 ·
ggenelly said:
Why wouldn't you want heat in the back too? Anoth GMC issue with these vans...
Depends on where you live. You don't want it on when you are in hot weather... or using the air conditioning. With it constantly on there would be a constant hot heater core in the van. Mine works very well with new vacuum lines and I was glad it was off today.
 
#10 ·
I'm a little late to the party but I wanted to comment on what I've learned about the heater situation in Astros.

Apparently there are (at least) THREE styles. I'm not exactly which years have which style.

STYLE 1) Hot water is always present in the FRONT passenger side, inside cabin heater core. The dash controls ONLY open and close the vent doors. With the heater off, you STILL have a 200 degree box of water sitting under the dash, a couple inches from the passenger's feet, even in summer.

STYLE 2) Valve controls hot water to the passenger side, FRONT inside cabin heater core. A vacuum operated valve shuts off the water to the FRONT heater core. Now when you have the dash heater control set to off, hot water is BLOCKED from flowing to the passenger's feet area.

STYLE 3) Valve controls hot water to the REAR heater core. This is present with either of the above styles (or there may be no rear heater at all). A vacuum operated valve shuts off the water to the REAR heater core. When you activate the REAR HEAT switch on the dash, that valve opens, hot water flows to the rear.

There are likely other variants.

In MY setup, and Maher's, we originally had the #1 style. Hot water was always present in the front heater core. In my case, in Phoenix, we use the heat for maybe ten days out of the year. When it's 110 degrees outside, and 123 in the closed cab as you get in, you really don't want an additional 200 degree water box in the cab with you. So I installed a simple shut off cock on the water line that flows TO the heater core. I open the valve during the very short cold season, it's closed the rest of the year (open it once a month just to keep water from getting stagnant).



Lump
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top