My heater only blows through the A/C vents when.

Check the mode door actuator. Try going into self-diagnostics to check for trouble codes.

Entering Self-Diagnostics

1. Start engine. Using a jumper wire, ground self-diagnostic test lead. See Fig. 4. Auto amplifier will enter DIAGNOSTIC STEP 1 of self-diagnostic procedure.

2. To proceed to next DIAGNOSTIC STEP, press HOT switch. See Fig. 3. To return to previous DIAGNOSTIC STEP, press COLD switch.

Exiting Self-Diagnostics

To exit from self-diagnostics, turn ignition off and disconnect self-diagnostic test lead connector ground. See Fig. 4.

DIAGNOSTIC STEP 1

Indicator & Switch Inspection

1. Indicator lights should flash and temperature display should indicate -188 (all segments lit). See Fig. 3.

2. If indicators DO NOT flash, or temperature display does not indicate -188, replace auto amplifier. If indicator lights and temperature display segments are okay, go to next step.

3. Press HOT switch. Temperature display should indicate 2. Press COLD switch. Indicator lights should flash again and temperature display should indicate -188. This indicates proper operation of HOT and COLD switches.

4. If switches are okay, go to DIAGNOSTIC STEP 2. If switches are not okay, replace auto amplifier.