Primary fan will not come on. If I ground relay terminal fan runs fine. Aux fan runs with air on. Temperature guage never goes much beyond half way, even when overflow boils over. Replaced ECT-temp sensor with Volvo ECT-temp sensor(twice) and no change. New thermostat. If I disconnect ECT-temp sensor with engine running, ECM does run primary fan continuosly in error mode with MIL light on. I have temporarily installed aux relay to ground primary fan relay when ignition is on.

Any suggestions??????

 

I am having trouble trying to figure out what you are referring to as the "Primary Fan" and the "Aux Fan". There is one blower that has two speeds. The fan relay, via instructions from the ECU, tells the blower to run and what speed to run at. On the center connector of the fan relay there are two wires, a yellow wire and a yellow/white wire. One wire chooses low speed when grounded and the other chooses high speed when grounded. I can't remember which wire color chooses which speed off the top of my head but you can hear the difference in speed.

Ground the relay pins on the middle connector on the fan relay, one at a time, and you should get both fan speeds to operate.

During normal operation the coolant can boil over if the system is not pressurizing. A crack in the overflow tank or a bad radiator cap an keep the system from pressurizing.

...Lee

 

Aux fan is the one controlled by AC system, primary is contolled by ecm and temp sensor(ECT). I can ground either of the pins you refer to and the fans run. The primary fan never comes on. Before this problem the fan would run during operation and for a minute or so after engine is shut down.