I just replaced a seized electric fan with a salvage fan that is good. Tests on the bench just fine but does not power up in the truck when the A/C is switched on. Checked the 40A red fuse (it was good) and swapped the yellow fan relay in the under hood fuse box but still does not turn on. Used a meter to check for 12V power at the connector and there is none. Ideas?

 

It will only turn in when the AC needs it. It doesn’t always come on instantly upon turning the AC on.

 

Block the rad with a plastic bag temporarily pressures should rise in the ac system providing power to your fan

 

Or try putting a hairdryer on the temp sensor near the condensor, tricking the ECU into thinking it's hot out? I think there's more than one sensor to trigger HVAC, but that may be enough.

 

System won't turn on the fan unless it's over 76 degrees. Also a speed sensor somewhere that turns it off on the highway

 

OK, so unless the hairdryer only goes to 76°, and you have the truck on a 4 wheel dyno simulating highway speeds, I think it's still a valid test.

 

You are correct

 

At least we're on the same page then

 

Yep just giving him a temp to shoot for

 

Just jump the relay for the fan.