I have a 2000 XJ and have a few things going on involving the heater and not sure where to start. First, the AC works fine and blows cold air at a good speed, but when I switch to hot air, the volume/speed of air coming out of the vents drops and will not blow hot air...its lukewarm at best. Also, when accelerating (3000 rpm), the air stops blowing completely even though I can hear the blower motor still blowing full blast. I have also noticed that this time of year, when its cold outside (20-40 degrees F), my engine temp going down the highway (60-70 mph) will not get above around 160-175 degrees. I installed a new 180 degree thermostat this summer, replaced the AC/heater relay and resistor, and flushed the heater core. I'm assuming the loss of air flow at higher rpm is a vacuum issue, but I'm not sure where to look/how to test it.

Any help appreciated.

 

anyone have any ideas?

 

1) since it dies when you accelerate sounds like you're losing stored vacuum. Check all the vacuum lines for leaks, check the check valves, check the vacuum can behind the bumper. It's Mityvac time
2) put in the correct (195) thermostat after you fix the vacuum leak.