rear heater blows cold air

I replaced the heater lines on my van. Thinking that the rear lines were plugged. I still don't have any warm air coming out of the rear heater. The fan works just fine. Someone says that it might be the heater control valve. Is there one for the rear heater only? I have good heat from the front heater.

I had the same problem with my 97. It traced it back to an electric switch that open vacuum to a vacuum valve on the hose going to the rear heater. The valve is located on RH side in engine compartment.

To troubleshoot, join the two vacuum hoses together (by pass the electric switch) with a plactic union and take the van for a spin. If you now have heat, the electric switch is at fault if power is reaching it.

Otherwise, the vacuum valve is defective.

I am having the same problem on my 96 astro. I pulled the small vacuum line off of the rear diverter valve and the air in the rear got hot. The problem is I now loose my defroster door control for the windshield. Where is the electric switch located. I cannot see it.

I am an owner of a 1998 Chevy Astro with rear heat and rear air. My problem was only cold air out of the rear heat and only the front defrost vents worked and the temperture selector not switching for hot to cold. I will try to be as detailed as possible. Lift the hood, and look at the large black box on the top left side of the engine. Just behind the AC reservoir, there is a vacuum line attached to the large black box on top right side, that looks like a Tee fitting with three connections. One went to the float switch on the bottom right of the larger black box, the other goes straight down to the vacuum ball located on the frame of the vehicle (underneath). The last is a thin vacuum line that looks like an electrical wire. Pull on all three lines one at a time. If one pulls all the way up to you, that is the broken one. The thin wire was broken in half on my Astro. The fix was to remove the air filter tube (the 3" flex tube that goes to the air filter box). Once removed, look for a flexible black tubing about a 1/2 inch round that should look empty because your line is broken. Pull the tubing to reveal the other half of the hose and reconnect with tubing that will fit over the thin blak wire. Not sure what size, but what I did notice is that this was probably the same problem that GM fixed before when the vehicle was under warranty because my line looked repaired but was broken in a different spot. Before I reinstalled the air box tubing, I did wrap the entire flex tubing line with aluminum foil to help block the heat. I am not a professional, but I tried this and it worked for me. Good luck. This feels like the scene in Independence Day when they figured out how to bring down the spaceships in the sky. Good luck.