Ford Ranger 2004 ECU not letting AC work

[smswedenburg]

I was informed by Firestone I need a new ECU on my 2004 Ford Ranger because it not enabling a relay for the Air Conditioning.
They wanted $650 for the ECU and $350 for the install and programming.
I found a replacement ECU at www.fs1inc.com for $131.25.
I have a OBD2 adapter and laptop.
Besides the VIN and shift parameters what else do I need to copy over?
Is the ECU really wounded or was I fed a line?

 

[RonD]

It is "possible" the PCM could keep AC from cycling on, but it would be a long shot.

Need to know engine size, and I assume Automatic Trans from your other statement, to see exact wring diagram.
And when you say AC doesn't work do you mean Compressor is not cycling on and off or that the Blend door in the cab isn't letting cool air blow thru the vents?

AC still works the same as it always did, there are high and low pressure switches on the freon lines that both must be closed(Grounded) or compressor won't cycle on.
The AC relay's coil gets 12volts when key is on, but has no Ground so doesn't close to turn on compressor.
Ford decided to run that Ground thru the PCM and THEN to the AC relay.
When you turn on the AC that signal goes to PCM, not AC relay
The PCM then looks at engine coolant temp(3.0l/4.0l) or Head temp(2.3l), before Grounding the AC relay(turning on compressor).
If engine is overheating it will turn off AC compressor

PCM will also unGround the AC relay when Throttle is wide open, TPS above 4.5volts.

If the CEL isn't on and so there are no codes then it could be the PCM is not passing the Ground to the AC relay when it should be.

Not sure what you mean by OBD2 adapter?
Reader or scanner can't program a PCM.

Tweecer or Moates sell tuners, but not sure they can change automatic software

 

[black_demon69]

check all fuses NOT ALL FUNCTIONS are listed in manual and fuse may be blown.

 

[adsm08]

It is technically possible, but extremely unlikely that the PCM is causing the issue.

If your setup does live data you should be able to see if the switch is registering as being on, and then jumper switches to see if the system can work.

Last time someone brought me a vehicle because the AC didn't work and a Firestone-type shop told them it needed a PCM I fixed it with a $25 cycling switch.

 

[97RangerXLT]

Agree with all of the above. check to see if your refrigerant is low. that is the first thing I would look at. if it is too low the switch on the low side will not close and the pcm will not allow the compressor to run (works as it was designed to do to save your compressor)

Your static pressure should be around 70psi when off, and may dip as low as 15 or 20 psi on the low side when running dependent upon the outside air temp and elevation above sea level.

AJ