A/C Evaporator - Icing Condition: Overview
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1986 GRAND WAGONEER J/10 AND J/20 TRUCKS
AUGUST 1987
HEATING AND AIR CONDITIONING Attention: Workshop, Parts Department
EVAPORATOR ICING CONDITION
Evaporators on some early production 1986 Grand Wagoneers, J/10 and J/20 trucks may have a problem with the A/C unit putting out extremely cold air for a time, then, gradually warming up until only ambient air is emitted from the air ducts.
Possible Causes
This problem may be the result of evaporator icing. There are two possible causes of this evaporator icing condition:
1. An incorrectly calibrated temperature control module (TCM), and/or
2. A thermistor probe which has shorted-out.
NOTE: Depending on the heat and humidity, condensation can enter the thermistor probe (thermocouple), causing the thermistor probe to short out and cause the compressor to continue operating. Once the condensation has evaporated, the thermistor probe will usually operate normally again. This normal operation may continue until water re-enters the thermistor probe. Then, the evaporator will ice up again.
Possible Corrections
Service correction involves:
Inspect for a correctly calibrated TCM. This is the first item to check when evaluating for an evaporator icing condition.
If the TCM is not marked with one of the two sets of numbers indicated in the following TCM servicing procedure, then, replace it with a correct unit.
If the TCM is calibrated properly, then replacement of the thermistor probe is necessary.