1996 Dodge Caravan blinking lights

To incorporate all the toys and gimmicks people demand today, the engineers can justify hanging a very unreliable, trouble-prone computer onto every imaginable system in our cars. '96 was the first year to find a computer on the Caravan heater system.

When the battery is disconnected or run dead, the memory was lost in the computer. That's what the flashing lights are telling you. Calibration tests must be run. To pass the second half of the procedure, the air conditioning must be working properly, but it can still be very frustrating to get it to pass.

Here's the procedure from the service manual minus all the pages of diagnostic tests:

ACTUATOR CALIBRATION/DIAGNOSTICS AND COOLDOWN TEST
GENERAL INFORMATION
If the HVAC control module is replaced, the Calibration Diagnostic and Cooldown tests will need to be performed. Once this group of tests have successfully passed, they can be performed individually. The engine must be running during the test to provide hot coolant for the heater, A/C compressor operation and to assure that the actuators are calibrated correctly. The HVAC control module is capable of troubleshooting the system in approximately 120 seconds. If a condition is detected, an error code is displayed. The error code cannot be erased until the condition is repaired and the diagnostic test is preformed. Check wire before replacing components, Refer to Wiring diagrams
CAUTION: Do not remove the actuators from the Heater-A/C unit assembly with power applied. Removal should only be done with the Ignition OFF. The actuators have no mechanical stops to limit the travel. If the actuator rotates and is not connected to the unit assembly, it will become out of calibration.
CALIBRATION/DIAGNOSTICS TEST ENTRY
TO INITIATE TESTS:
"Â Set Blower motor ON HIGH
"Â Set Mode position to Panel
"Â Set Temperature to Cold (Both slide pots if equipped)
"Â Depress WASH and REAR WIPER button simultaneously for 5 Seconds (Until all LED's light)
RESULTS:
"Â All LED's will turn on for 5 Seconds
"Â Calibration Test is running when REAR WIPER and INTERMITTENT are alternately flashing. Cooldown test is running if A/C and RECIRC are alternately flashing.
"Â Acceptable results is REAR WIPER LED is the only LED flashing. Push Rear Wiper to exit.
"Â After all tests have passed, Calibration Diagnostics and Cooldown can be run separately.
COOLDOWN TEST ENTRY
TO INITIATE TESTS:
"Â Set Blower motor ON HIGH
"Â Set Mode position to Panel
"Â Set Temperature to Cold (Both slide pots if equipped)
"Â Depress WASH and A/C simultaneously for 5 Seconds
NOTE: If the evaporator is already cold, operate system with A/C OFF and the blower motor ON high for three minutes prior to starting test.
RESULTS:
"Â All LED's will turn on for 5 Seconds (Until all LED's light)
"Â Cooldown Test is running when A/C and RECIRC. Are alternately flashing. If A/C and RECIRC. Are flashing simultaneously, Cooldown has failed. Make sure that the Blower motor is ON high, and temperature is ON full Cold, abort test and repeat Calibration Diagnostic and Cooldown test again.
"Â Calibration Test is running when REAR WIPER and INTERMITTENT LED's are alternately flashing.
"Â After all tests have passed, Cooldown test can be run separately.
"Â Acceptable results is REAR WIPER LED is the only LED flashing. Push Rear Wiper to exit.
CALIBRATION DIAGNOSTICS AND COOLDOWN ABORT
Test can be aborted by doing one of the following:
"Â Depressing Rear Window Defogger, RECIRC and Rear Wiper buttons.
"Â Cycling Ignition OFF and then ON.
"Â Control will automatically abort after 15 minutes from the time Calibration Diagnostics and Cooldown was entered.
The HVAC control module will return to normal operation or may indicate unsuccessful Calibration Diagnostics or Cooldown test by LED's flashing simultaneously.
NOTE: Do not run actuators unless they are properly mounted on the HVAC control module.

Ok, without rereading all of that, one thing they don't mention is if the cooldown test doesn't pass, start with the temperature set to "hot" then slide it to "cold" right AFTER starting the cooldown test. If that doesn't help, do the same thing right after driving a few miles at highway speed to increase the coolant temperature. It's not uncommon for it to take 20 tries for this test to pass.

Caradiodoc