I have swapped a 5.4l 3V from a 2008 F-150 into my 62 f-100, I have the engine running, but when it comes to the A/C system I have a few questions.

I am trying to use a simple underdash unit with all the factory a/c stuff from the 08. My main question is do I need to rely on the PCM to turn the compressor on, or can I bypass the PCM as far as the A/C goes, and still have the engine run correctly? Will the PCM still compensate with a high idle, etc, even if I bypass it?

I am pretty sure the answer to my first question is no, so I have another question also. I am using the Ford wiring diagrams, it looks like I could just send power to the A/C cycling switch, and the system would work correctly(as long as I keep the wiring the same as it was in the 2008 configuration)? So basically I would be using the underdash unit in place of the manual climate control system.

My reason for asking this question is because in the wiring diagrams it looks like the A/C cycling switch is getting power from the fuse panel in start and run, but i can't find anywhere else to switch power into the system so the compressor kicks on when needed?

Thanks in advance for everyone's help, it is greatly appreciated.

 

The mode/cycling/high pressure switch series circuit should signal the PCM that AC compressor operation is desired.

The PCM, when its programming permits, should then output a ground signal to the clutch coil relay that actually switches the clutch's power on and, when de-energized, off.

 

I'm pretty sure that answered my question. I'm gonna wire it up so the switched input goes into the a/c cycling switch and see what happens.

Thanks for the help.

 

I understand this, but I can't find a place to input a signal from my a/c unit to get this to work.

The a/c cycling switch has 2 pins, one is incoming power(fused), the other is the signal(ground) to the a/c clutch relay.

The a/c pressure transducer has 3 pins one is high pressure cutout signal to the pcm, one is "signal return", and the other is "reference voltage".

These are all based on the Ford workshop wiring diagrams.

I am looking for a circuit that would allow me to input power from my a/c unit into this system to get it to work.

I can find the a/c compressor request button signal, but it dead ends in the HVAC module, and I'm not using the HVAC module, so I was hoping for some enlightenment on this.

 

Do you want the PCM to control the AC or do you just want it to work?

 

I need it to work, as long as the engine runs correctly, higher idle, fan clutch controlled by a/c, etc.

Either way is fine with me, I have all the PCM stuff already wired up, except for the incoming signal, but if there is a simple way to "make it work" I'm up for that too.

Thanks

 

So, I found this tidbit of information:

The AIR CONDITIONING COMPRESSOR CYCLING SWITCH (ACCS) PCM PID reads ON when both of the following are met:

• the PCM receives an A/C request through the CAN bus.
• the PCM receives voltage from the A/C cycling switch.

I'm pretty sure I am not going to be able to use the PCM to control the AC because I'm not using the instrument cluster or the CAN bus system on this swap.


So, can I just switch power(or ground) to the AC compressor relay, and expect the PCM to do everything else when the AC is running, low pressure circuit, high pressure circuit, fan control?


Or do I need to just "make it work" like an old school AC system?


Thanks

 

Since you can't make it work through the PCM due to the CAN bus criteria, I suspect you might get some weirdness when the A/C is operating independently from the PCM. You'll likely notice it particularly at idle speed.

I'll see if I can scratch something up later today if you need it.

 

That's what I was thinking too. Let me know what you find, it will be greatly appreciated.

Thanks

 

How feasible would it be to get a cluster and a HVAC module and use just the a/c request switch and the CAN network wiring to the PCM? I am using my old gauges from 62, so I may be able to hide the late model stuff behind the dash, once I simplify them. Let me know if this is a crazy idea or not.

Thanks

 

Just thought of this as it may derail the project.

How are you planning on satisfying the PATS on the 08 PCM?

 

I already have it running, I had a custom tune made to remove the PATS.

I'm gonna wire the AC up old school style and see what happens. I think the CAN bus system will be too much of a pain in the *** to deal with, so I'll see how it goes, it might be a few weeks before I get this done, then I'll report back.

Thanks for all the time and help.

 

Good, didn't want that to be a show stopper.

I'd wire it up as follows:

Mode Switch (fused) > Low pressure > High pressure cutout > energize Relay.
When the relay energizes, switch fused (20A) battery power to the clutch coil. Don't forget the reversed diode across the clutch coil.

If using electric fans, I'd also set it up so that the energized relay (or control signal) also activates the fans on high speed.

The high-low switches may reversed, their order doesn't matter from an operational standpoint.