Cooling Fan Won't Shut Off - Not Relays - Page 2

writerman · 10-28-2009, 09:40 AM

I didn't notice any difference when I put the new DPFE on. I did get it from the dealer so at least it's OEM. I didn't replace the hoses when I put the new one on but I'll try that, especially since it's a cheap & simple fix. As for the EGR tube and ports, mine are clean. I just had it off about two weeks ago and checked it then. Small coating of carbon, but that's it. I think I'll order a new EGR vac regulator from Rock Auto and give that a shot.

BroncoJoe19 · 10-28-2009, 09:47 AM

Regarding your fans, how do you KNOW that the relays are good?

BroncoJoe19 · 10-28-2009, 12:12 PM

N76 is supposed to be the connection to the AC high low dual pressure switch. See if disconnecting it makes a difference.

AC-highLowSwitch.JPG

writerman · 10-28-2009, 01:54 PM

I don't, but I did purchase the hi & lo fan relays from my Ford dealer and swapped them out last night with no change. Was hoping that since they were brand new in the package that they were good.

I'll disconnect the AC pressure switch in the parking lot and see if it makes a difference on the ride home from work and report back. Thanks for the diagram locating it.

Cuda_Jim · 10-28-2009, 02:36 PM

Here's a little more info:

The fan control system consists of:

Powertrain Control Module (PCM).
Air Conditioning (A/C) pressure cut - off switch.
High speed cooling Fan Control (FC) relay.
Low speed cooling fan control (FC) relay.
Engine cooling fan resistor.
Engine cooling fan motor.

The powertrain control module (PCM) determines the cooling fan motor requirements and controls the fan operation through the low speed fan control and high speed fan control outputs. The PCM outputs complete the ground side of the relay coil circuits. Power to the relay coil circuits is provided by the PCM power relay.

If low speed fan operation is required, the PCM grounds the low speed fan control output. This energizes the low speed FC relay coil which closes the low speed FC relay contacts. Power flows through the fuse 2 (60A), the low speed FC relay contacts, the engine cooling fan resistor, and the engine cooling fan to ground. The engine cooling fan resistor provides thermal overload protection for the low speed fan control circuit.

If high speed fan operation is required the PCM grounds the high speed FC relay coil which closes the high speed FC relay contacts. Power flows through the fuse 2 (60A), the high speed FC relay contacts and the engine cooling fan to ground.

High speed fan operation may also be commanded by the dual pressure A/C pressure switch. The medium pressure contacts of the A/C pressure switch turn on the high speed cooling fan when A/C head pressure reaches a predetermined level grounding the air conditioning pressure switch. This grounds the high speed FC relay circuit. This closes the high speed FC relay contacts and turns on the high speed cooling fan.

If A/C head pressure drops below the predetermined level, the medium pressure contacts open returning the high speed FC relay operation to the PCM.

BroncoJoe19 · 10-28-2009, 03:09 PM

So If I am following this correctly he would look for a short to ground between the PCM and the high speed relay, ie the black/white tracer wire.

Great post Cuda!

Cuda_Jim · 10-28-2009, 04:18 PM

Joe, that's what I was thinking when i read it. Hopefully he'll let us know soon.

writerman · 10-29-2009, 11:50 AM

Okay, so I disconnected the N76 connector and the fan never came on. Hooked it back up and after a few minutes on came the fan and never shut off. So, is the switch bad or do I have a short somewhere? And what do you suggest I do next?

BTW, thanks in advance for all the legwork helping me track this down.

Cuda_Jim · 10-29-2009, 12:31 PM

Quote:

Originally Posted by writerman

Okay, so I disconnected the N76 connector and the fan never came on. Hooked it back up and after a few minutes on came the fan and never shut off. So, is the switch bad or do I have a short somewhere? And what do you suggest I do next?

BTW, thanks in advance for all the legwork helping me track this down.

It's likely there is no short to ground because it took a few minutes for the fans to come back on.
IMO, A short would immediately turn them on.

My guess is,
1. most likely the switch is bad
2. there is a restriction in the system causing higher than normal head pressure
3. Least likely, it's just slightly over-charged.

An AC Tech would know for sure.

BroncoJoe19 · 10-29-2009, 12:37 PM

So, is the switch bad or do I have a short somewhere
IF there is a short it is probably between the connector and the AC switch, or the switch is bad. You can try starting it up, wait for the fans to come on, and then wiggle the wiring harness. If the fans go off, then the short may be in the last section wiggled. IF NOT... then I guess the switch is bad.

I know nothing about changing the switch, ie if it will leak freon etc.