My 2000 Grand cherokee only blows warm air from defrost or any vent, 105 to 110 on a 32 degree morning with high fan, about 10 degrees warmer on low fan. It gets warmer when it warms up outside.Engine temperature stays around 200.Have replaced thermostat, water pump, heater hoses, and flushed the heater core. The dealer repaired the blend doors, they seem to work right.
You talk about blend doors, so i suspect you have the Automatic Zone Control system. Did you check the system for any fault codes? When defrost is selected, the airco will automatically switch on as well to reduce the humidity of the air (independent of the airco switch). So also the air will become less hot. But when the other air outlets are used, the airco should not work. Did you check if the airco is off in other then defrost mode?
With the manual controls, there is only one blend door/ actuator. You can access it by removing the glove box. You said the system was repaired by Jeep, but you never know. You could remove the actuator and see if you can rotate the door by hand without sticking or binding. If the door is ok and the actuator is moving over the full range, there could be some restriction in the liquid flow to the heater core. I think you told that you had changed the heater core hoses, didn't you? Was that for the same problem of low heat?
I changed the heater hoses and water pump to see if that would help with the heat. It made no difference. The door for the heat seems to work fine when I remove the motor. If i use recirculate for heat it gets warmer, about 135 in low fan speed.
When you start the engine in the morning, did you try to feel both heater hoses, to see if both heat up equaly? You did flush the heater core, any feel of obstruction thru the core? You checked the blend door by removing the actuator, did you also saw the actuator moving the door to full open when hot was selected?
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