I warm my van up in the morning before I go to work & the heat works just fine. When I get to a stop sign or a red light the heat turns to cool air. I can put my van in park & press the gas peddle & will get heat right way. This has been happening every day for about a week now. It doesn't do it all the time just randomly.

The other day I was getting hot air through the all the vents in the front but the vent by the driver windows. That was blowing cool air. I put my van in park when I got home & checked the rear vents & they where barely blowing any air & it was cool air. This has only happen once w/the 1 vent blowing cool air.

Any ideas what is going on??? I have a 2005 GC.

 

One possibility is that your thermostat is not cycling correctly, at start the stat is closed and at programmed opening temperature the stat fully opens, then continues to follow the temperature, as temp starts to fall off the stat closes a bit and as it reaches temperature it opens fully, in your case the stat my open and then not correctly close so the temp is falling off until at some point the stat says whoops and starts to function correctly (for a bit).

 

Ck the coolant level, if its low you may have leak.If the coolant level is full, I would recommend a t-stat.