Engine Fan only runs with A/C on

[Tippy280]

After changing a broken thermostat housing, I noticed the radiator cooling fan will only operate with the A/C on. While sitting in traffic with the A/C off, the car will begin to overheat because the fan is not automatically coming on. This is my daughter's car and not driven very often, so I don't know how long this has been going on. I sense it is either a relay, or a cylindar heat sensor. Any help is appreciated. Thanks.....

[Davescort97]

Welcome to AF. The Constant Control Relay Module (CCRM) contains the relays for the high and low fan speeds. The same relay that turns the fan on for the A/C is used for temperature sensor so I would say that the relay is all right.

The PCM (Powertrain Control Module) determines when fan operation is required by monitoring engine coolant temperature and the air conditioning status. When operation is required the PCM signals the fan to turn on to the desired speed.

There are two temperature sensors in the thermostat housing. One for the gauge on the dash and one for the PCM. I believe that the sensor for the gauge has just one wire and the sensor for the PCM has 2 wires. Check the connector on the sensor. If it is all right I would suspect that the temp sensor for the PCM is defective.

[Tippy280]

Originally Posted by Davescort97

Welcome to AF. The Constant Control Relay Module (CCRM) contains the relays for the high and low fan speeds. The same relay that turns the fan on for the A/C is used for temperature sensor so I would say that the relay is all right.

The PCM (Powertrain Control Module) determines when fan operation is required by monitoring engine coolant temperature and the air conditioning status. When operation is required the PCM signals the fan to turn on to the desired speed.

There are two temperature sensors in the thermostat housing. One for the gauge on the dash and one for the PCM. I believe that the sensor for the gauge has just one wire and the sensor for the PCM has 2 wires. Check the connector on the sensor. If it is all right I would suspect that the temp sensor for the PCM is defective.

Thanks so much for the suggestion, but I believe I found the problem with the resistor pack. Although the resistor pack itself checks fine with a voltmeter, the plug going to it had bad burn marks on the connection which was also cracked. Now I am just wondering if I should crimp on some new connectors on the two wires and heat shrink them or replace the whole connection harness which since it is Sunday, I have no idea what it costs or entails to change. Thanks for any further suggestions.

[Davescort97]

You could crimp on new connectors and if that solves the problem you are done. The wiring harness could come later if you need to go that route.