heater doesn't work properly on 2007 Saturn Relay

The front heater will blow hot but when you stop for a light it will start blowing cold but will again blow hot when you speed up and the rear heater never blows hot. What could cause this problem?

by in Silsbee, TX on October 28, 2012
2 answers 2 comments
ANSWER by on October 28, 2012
MAKE SURE IT IS FULL OF COOLANT. HOW MANY MILES ON ODOMETER?
COMMENT by on October 29, 2012
It is full of coolant. I even took the cooling system cap off and added water, which was only about a cup full at the most. The van has approx. 93000 miles on it.
ANSWER by on October 29, 2012
sounds like coolant level is low ck that 1st thing
COMMENT by on October 29, 2012
I checked by removing the cooling system cap and added water to the system there, which only held about a cupful at the most.