My AC recently quit working.

I have verified the actual clutch is functional [using a ac clutch plug-pigtail, I jumpered direct to the starboard battery].

I have also made a jumper to bypass the high pressure switch to test the clutch but the clutch still did not engage.

This makes me suspect the relay and the cycling switch.

Background research:
I've heard guys mention the high pressure switch and that there's no relay... but I'm looking at the shop wiring manual and it appears there is a relay,, and there's also another switch in series, called the A/C compressor cycling switch [N75]. Also, it appears this circuit passes through the PCM. I am guessing the info i heard was for an older model.

- Any of you have experience with the relay failing? And where its located?

- Any of you have experience with the cycling switch failing? And where its located?

- Also, have any of you seen the A/C Clutch Diode [V7] fail to short [Fail as a short to ground]?

What fails most often, in your direct experience?:

1. N126 A/C high pressure switch [19D594]
2. N75 A/C compressor cycling switch (19E561]
3. P82 Function selector switch assembly, front 11) mode switch
4. PCM
5. K107 A/C clutch relay [in P114 Auxiliary relay box 4]
6. V7 A/C compressor clutch diode [located in the CJB [inside fuse panel, under steering wheel...it has relays and diodes buried on the back side]



Page 54-1 [air Conditioner/Heater] of the 2002 Wiring Diagram, Excursion, F-Super Duty, 250, 350, 450, 550


Here's a refresher [hah, pun] for anyone wanting a reminder of how the system works, theoretically, from the 2002 shop manual [volume 1, page 412-00-06]

2002 ford f-super duty Shop Manual, volume 1

 

I thought these might be helpful for this thread, they include the manual AC [mine, btw, is the manual version that came with the XLT] and the fancy automatic climate control. :-)

 

You can check continuity across the low side (cycling) switch. It should be closed with the compressor off at ambient temps above freezing (approximately). But I have to guess if it was near freezing, you probably wouldn't be messing with the A/C, lol.

 

I am gonna check that relay. I have had water intrusion problems with the aux relay boxes outboard of the brake master cylinder before... they are always suspect to me :-)

 

Before you replace any switches or relays, have you checked your refrigerant level? How about the clutch's air gap?
To answer your question, I have had high pressure and low pressure switches fail equally often. All other AC-related electrical components not so much.