TEST OR INSPECTION
1. HEATER DOES NOT ENERGIZE
Heater will shut down automatically if vehicle voltage drops below 21 volts. If heater
does not start in three minutes, start switch will automatically shut off.
Step 1. Check for proper voltage requirements as follows:
a. Disconnect switchbox cable (1) to heater (2).
b. Using multimeter set to read dc voltage, put red probe on terminal 30 and
black probe on terminal 31 of switchbox cable (1).
If multimeter reads anything other than 21 volts to 28 volts, troubleshoot
vehicle electrical system (refer to applicable vehicle technical manuals),
Step 2. Depress the overheat reset button (3) on the switchbox (4).
Step 3. Replace Air/Heat switch of switchbox. (refer to applicable vehicle technical manuals).
Step 4. Check switchbox cables (1) and (5) for broken, corroded, or missing terminals as follows:
a. Disconnect switchbox cables (1) and (5) from heater (2).
b. If corroded, broken, or missing terminals are found, clean or replace (refer to
applicable vehicle technical manuals).
Step 5. Replace heat regulator (page 3-179).
If heater still does not energize, replace heater.