Aux fan works when jumped, changed switch and still nothing

[ZeKahr]

It doesn't matter if your fan thermo switch is good or bad, if the fan works at all on low speed the AC will turn it on, the thermoswitch is bypassed in this scenario. Download a copy of the ETM, knowing how things are wired will help.

There is a diode in the line leading up to the fan relay to prevent the thermoswitch circuit from backfeeding and turning the AC compressor on, unfortunately I don't know where the diode is located. If you find it do post about its location so future searchers don't have to explore for it too.

From looking at the ETM and from some forum sleuthing I’ve done, it looks like the diode is located inside the fusebox, underneath all the fuses and relays. He’ll have to open up the fusebox itself to get to it.

[tomstin]

Does the AC compressor kick on? If not, the vent mixing sliders need to be in the correct position and the sensor to protect the evaporator needs to be functioning before the compressor and fans kick on.

There is also the circuit for an overheat or high temperature situation for the aux fan to come on. So, check those sensors.

[varg]

It doesn't matter if your fan thermo switch is good or bad, if the fan works at all on low speed the AC will turn it on, the thermoswitch is bypassed in this scenario. Download a copy of the ETM, knowing how things are wired will help.

There is a diode in the line leading up to the fan relay to prevent the thermoswitch circuit from backfeeding and turning the AC compressor on, unfortunately I don't know where the diode is located. If you find it do post about its location so future searchers don't have to explore for it too.

[snowfox]

Found this write up on another forum and this diode seemed to fix his problem, but no instructions on where it is or how to find it! Anyone have experience with this and a part number?

[reelizmpro]

Don't assume that. Jumping the connector with a wire is different than 30 year old female terminals mating to male terminals. I've bought numerous switches because I assumed that and eventually had to replace those female terminals. I'm guessing they open up over time and fail to make proper contact plus corrode.

[snowfox]

I replaced the switch with a brand new one and still nothing. If it works jumping it then I assume the connections are good?

I believe cooling system is full and bled, but even if it wasn’t the fan should kick on with the AC button and it’s not.

[reelizmpro]

Then the fan and resistor are good. The problem is either the switch or the connection to it. This is assuming the cooling system is full and properly bled. Corrosion occurs and sometimes contacts need to be cleaned or replaced.

[snowfox]

Hi all,

I’ve seen a bunch on this topic, but haven’t come across my specific issue yet.

My Aux fan does not run. When I jump it at the temperature switch I it runs great in BOTH low and high speed. I swapped out the switch today and still don’t get any fan activity when I turn the AC on.

My question - will the fan run in both high and low if the resistor is bad? Im knew to this, but it sounds like if the resistor was bad then it wouldn’t run in low speed when jumped. Should I change that out next or what other trouble shooting should I do?