I can't find the heater control valve

GREG V

MEMBER
1998 JEEP WRANGLER
55,000 MILES

ASE tech Greg here. All obvious preliimanary checks show perfect. Have not touched or flushed yet. 55 K mile 98 flawless Jeep Wrangler 4.0 with both heater core hoses ice cold w/ engine warm. Makes no sense for solidly blocked core. No visible vacuum controlled coolant shut off valve in engine compartment. Does plenum box area inside cab have a vacuum controlled valve somewhere ? A vacuum hose routing chart should solve this mystery if you ave one handy. Thanks in advance, Greg

1 Reply

JACOBANDNICKOLAS

MECHANIC
108,331 POSTS

The vehicle doesn't have a heater control valve. It uses a blend air door. I would recommend flushing the heater core. Also, if you need to calibrate the blend air door, here are the directions. NOTE: Since both hoses are cold, my guess is the heater core is plugged.

1. With the ignition switch in the OFF position, move the temperature control to its middle (12 o'clock) position.
2. Turn the ignition switch to the ON position (do not start the engine).
3. Within 10 seconds of turning the ignition switch from the OFF to the ON position, perform the following rotations (sweeps) of the temperature control.
A. From the 12 o'clock position, rotate the temperature control counter-clockwise to the full cold position. Pause one second.
B. Rotate the control clockwise to the full hot position. Pause one second.
C. Rotate the control counter-clockwise to the full cold position. Pause one second.
D. Rotate the control clockwise to the full hot position. Pause one second.
E. Rotate the control counter-clockwise to the full cold position.