warm as it normally as it usually get in the van for that distance and temp??/ stuck my hand around the back side of the drivers seat and it was blowing 
cold air ??/ So my question is has the rear heater / Ac have a relay along with a solenoid in the rear unit that changes the cold to hot air flap??/ 
I wouldn't think it would have a vacuum system running to the rear of the vehicle but who knows 
[-o< 
Okay figured out that its probably the water control valve on the firewall under the dryer accumulator and GMpartsgaint with my VIN# says its a 6 port valve because of the rear heater/AC I guess ??/ But there calling for another valve that I have have been able to locate in any of the literature that I have searched see below ??/
Valve in question // So I still don't know what or where this other valve there calling for GM Part#15070012
15070012 VALVE,AUX HTR WAT SHUTOFF(2 PORT, TO REAR HTR, INCLS ACTUATOR/SOLENOID & MTG BRKT)
LM1(C36)(EXC YF7) 01 $155.22 $89.53
Valve under hood under dryer on the fire wall // See Pic below ??/
15984154 VALVE,HTR WAT BYPASS(6 PORT)
LM1(C36)(EXC YF7) 01 $83.95 $46.95