Electric Cooling Fan Full Speed Constantly

[brianzero]

Hi All,

I was wondering if anybody has had and or solved an electric cooling fan that is stuck on full speed all the time (while the key is in the on position and while the engine is running)?

I would think that there may be a relay stuck in the closed position, weak ground, or something like that. Or where would you start looking?

 

[Midwestdrifter]

I assume you are talking about the radiator electric fan, and not the AC/heater blower fan.

The ATC (AC control heat unit) will drive the cooling fan to full speed under the following conditions

AC system pressure high (or sensor failed)
Coolant temperature high (or sensor failed)
Loss of communication with ECM (no engine temp info, so it defaults to hot)

The fans relay could also be stuck.

 

[brianzero]

I assume you are talking about the radiator electric fan, and not the AC/heater blower fan.

The ATC (AC control heat unit) will drive the cooling fan to full speed under the following conditions

AC system pressure high (or sensor failed)
Coolant temperature high (or sensor failed)
Loss of communication with ECM (no engine temp info, so it defaults to hot)

The fans relay could also be stuck.

We can eliminate high coolant temperature (in my case). The temperature gauge is fully functional, so that sensor and the ECU are probably talking?

I suspect the AC control unit. The thing only works at its highest setting (full blast AC interior fan speed).

 

[Midwestdrifter]

The lack of low speeds on the HVAC blower is probably a failed resistor pack (not part of the ATC).

A good scanner can connect to the ATC and read its codes and status. If there is a communication problem you will see a code. Look at the AC pressure value, if its high, then you know the sensor or wiring is at fault.

You can remove the fan relay from under the drivers seat, and test to see if the contacts are stuck/welded closed.

 

[brianzero]

Very good advice, and ill start testing those relays. Ill report back when i find more.

 

[RedRabbit]

Brianzero, i am interested in your results. My 2005 T1N heats and cools, but as of a couple of weeks ago the blower fan doesn't work on any of the slower speeds, but if you set the fan switch to Max, the blower cranks up and runs full speed. Bottom line, it either runs wide open when the switch is in the Max position, or doesn't run at all and I just have flow-through air if the switch is in any of the slower speed positions.

 

[brianzero]

I checked out that relay and it opened and closed just fine, so my problem is most probably the air conditioning and heater control unit in the cockpit. What I should probably do it blast the unit out with deoxit and attempt to clean the internal contacts. That might give me control over that fan.

 

[autostaretx]

Brianzero, i am interested in your results. My 2005 T1N heats and cools, but as of a couple of weeks ago the blower fan doesn't work on any of the slower speeds, but if you set the fan switch to Max, the blower cranks up and runs full speed. Bottom line, it either runs wide open when the switch is in the Max position, or doesn't run at all and I just have flow-through air if the switch is in any of the slower speed positions.

99% of the time, that symptom is due to a failed resistor block ... it's a ceramic lump housed in the cabin air box but (easily) accessed from under the hood. (see inset photo)

Sometimes it's just the thermal fuse, which can simply be "jumped" (although a new fuse is recommended).




--dick

 

[brianzero]

Sadly, Im not going to be that lucky. My resistor had been changed and is still in good shape.

 

[RedRabbit]

Thanks very much for the recommendation to check the resistor block and fuse, Autostaretx. I will check that shortly. I don't long-term jumper fuses, too many years working electronics to want the smoke to wander around freely. And since my vent control knob is difficult to turn I plan on lubricating it, as well.

 

[Spencermobile]

Sadly, Im not going to be that lucky. My resistor had been changed and is still in good shape.

Have you had any luck with a fix?

 

[RedRabbit]

Have you had any luck with a fix?

I almost got the resistor block out and it started raining (heavily). I haven't been using the van much since Covid-19 started, but plan to complete removing the resistor block soon. Once I do I plan to check resistances across the pins on the connector and compare readings of the old versus the new, and will post here.

 

[Hellshalfacre]

Hey Brian Zero, not sure if you checked this yet but under normal circumstances if you were to remove the connector from the Hp switch on top of the filter dryer with the AC on, your condenser fan will energize on high. Check your connection there. It could be open or unseated.