Hi,
You have a non functioning heater valve. This valve will probably be on one of the coolant lines going thru the firewall to the heater core. The valve could be stuck or the vacuum lines that control it aren't holding vacuum. If it is vacuum operated, pull the vacuum line from the vavle and check for a strong vacuum with the engine running and the Climate control selector on either VENT, HEAT, or DEFROST.
BTW, You're welcome to join us in the Cherokee, Wagoneer & Liberty forum for answers to future Grand Cherokee questions :mrgreen:
-Nick :!:
