Issues with heat 99 TJ 2.5 L

[Joe_Daddy21]

I have a 199 Jeep TJ with 2.5 engine. My issue is with my heat and it’s two-fold. My heat works well at fan speeds one and two. My blower doesn’t work at speed three, but I’m not too worried about that. The main issue comes with fan speed four especially while driving. The heat is very poor and it’s lukewarm at best. I believe my water pump works fine since it gets to operating temp and stays there, and since I get heat at 1 and 2 I don’t think its the heater core.

The second issue is that when driving at mid-higher speeds (about 50-60) then vents will shut and switch to the defrost until my rpms come back down and speed drops.

Any help is greatly appreciated.

 

[Jerry Bransford]

The vents shutting off & switching to defrost while accelerating/driving at faster speeds is caused by a vacuum leak. Vacuum is what drives all the controls and if the HVAC system doesn't have enough vacuum the door flappers get wonky.

Your #3 fan speed not working is very likely from a bad resistor pack. The resistor pack works on speed 1-3, it is bypassed for the highest speed setting. When one of the resistor pack's resistors goes bad, that fan speed stops working. It could also be caused by a melted wire or bad fan switch but usually it's the resistor pack which is located behind the glove compartment door.

And poor heat output is most commonly caused by a clogged heater core. Coolant flows through the heater core 100% of the time and it can get clogged. Flushing the heater core back & forth with a garden hose is normally all that's needed to restore it back to good operation. Disconnect the two hoses that pass from the firewall on the passenger side to the water pump and flush it out... back & forth until you get good water flow in both directions.

 

[Joe_Daddy21]

The vents shutting off & switching to defrost while accelerating/driving at faster speeds is caused by a vacuum leak. Vacuum is what drives all the controls and if the HVAC system doesn't have enough vacuum the door flappers get wonky.

Your #3 fan speed not working is very likely from a bad resistor pack. The resistor pack works on speed 1-3, it is bypassed for the highest speed setting. When one of the resistor pack's resistors goes bad, that fan speed stops working. It could also be caused by a melted wire or bad fan switch but usually it's the resistor pack which is located behind the glove compartment door.

And poor heat output is most commonly caused by a clogged heater core. Coolant flows through the heater core 100% of the time and it can get clogged. Flushing the heater core back & forth with a garden hose is normally all that's needed to restore it back to good operation. Disconnect the two hoses that pass from the firewall on the passenger side to the water pump and flush it out... back & forth until you get good water flow in both directions.

Thank you so much for the info and quick response. I’ll flush the core this week and see if that helps.

 

[Jeepers79]

I have a 199 Jeep TJ with 2.5 engine. My issue is with my heat and it’s two-fold. My heat works well at fan speeds one and two. My blower doesn’t work at speed three, but I’m not too worried about that. The main issue comes with fan speed four especially while driving. The heat is very poor and it’s lukewarm at best. I believe my water pump works fine since it gets to operating temp and stays there, and since I get heat at 1 and 2 I don’t think its the heater core.

The second issue is that when driving at mid-higher speeds (about 50-60) then vents will shut and switch to the defrost until my rpms come back down and speed drops.

Any help is greatly appreciated.

I'm having this exact same issue with the heat at higher fan speeds and the fan not working at speed 3. I've flushed my core. Someone reccomend on another thread to fill it with CLR let it sit 30 min and flush it again. Haven't tried that yet and its 2 degrees here lol