I just bought a 2001 Expedition EB, 5.4, rear AC (fully loaded) 122k, Very clean engine (Cleanest I've seen with this many miles). And noticed that the A/C wasn't working well after I drove it home. When I test drove it, it was a 75 degree day (First nice day we have had this year in upstate NY) and the A/C was "acceptable". It has all this fancy climate control, so I figured it must be working, being it was 75 outside by the dash readout and I set it to 68 and the ac was nice and cool. Anyway, I noticed a few days ago (On the next nice day) that the AC was actually quite warm after 20 minutes. I assumed at first that the clutch was not engaging due to low pressure. I bought a can of 134a and have a decent gauge (the hose/gauge that comes with the expensive cans at Advance Auto) but, it does me no good without the clutch engaged.

So, I looked up how to "trick" the clutch into turning on, and tried jumping the sensor wire (unplugged from the sensor), it didn't turn on! So I plugged the sensor back in and heard the idle change. So I am assuming there's enough freon in the system to at least kick it on. I looked at the harness going towards the compressor, and it looks melted, but I'm unsure if that's actually the wires to the compressor. So my question is this. Is it most likely that A) the wires are broken/melted or B) the clutch died on me, Or C) I'm missing something?

Also, is it common for the manifold to crack on these or more likely a broken bolt? I've got an exhaust leak around the pass side 2nd 3rd cyl. If it's a bolt, the warranty I have doesn't cover it, but a crack they do (and I don't want to leave my truck at the shop for days to find out the hard way lol - I'd rather know my chances ahead of time.)

Thanks for any help

Steve

edit:

I checked the ac diode, relay, and all ac related fuses. All are withing proper specs on my fluke. The relay is also actuating ( tested by applying power to the primaries and verifying n.o./n.c. operation)

 

HVAC FAQs, perhaps. See signature.

Exhaust manifold studs, probably.

 

Perhaps one can wasn't enough.

 

You cannot draw refrigerant into the system (with a simple can setup) unless the compressor is engaged.

 

Thanks everyone. Yeah I can't fill it without the clutch engaged. That's what I'm concerned with. Either what I see really is a melted wire (Does this happen on these motors?) or the compressor is junk? I still need to read that HVAC FAQ too

 

The clutch will engage when the pressure is high enough. The can will discharge into the system and raise the pressure high enough to engage the clutch. Once the clutch engages more refrigerant will be drawn in. I've done this literally hundreds of times and never had an issue unless something was wrong with the system.

 

However, if the system's electrical controls are busted and the clutch cannot engage, you're left standing there with a can of refrigerant in your hand.

Since he reported a high static pressure, well above the level needed for the cycling switch to close, the pressure in the system is not the issue, the lack of clutch engagement is.

FWIW, you can usually guesstimate that the static pressure will be a little higher than the ambient temperature in degrees F. Consult an R134A PT chart if you want a more accurate number. This means there's enough refrigerant the system to engage the cycling switch and subsequently the clutch, but it doesn't necessarily mean that the charge is adequate for normal operation. If the system is simply low, you'll get a compressor that "short-cycles".

 

Have you yet tested for 12v power at the compressor 2-wire clutch connector when the system is on?

 

I have kindof put the AC issue on the back burner. I'm pretty sure after testing it all that the clutch is bad. I feel that I should have a shop handle this since they will have the right tools and the reclaimer to empty/fix/fill the system. Thanks for the help though on that!

I did manage to tune it up today though. Took me 10 hours. I started with the intent of changing the plugs and coils and Thermostat (Had a temp code when scanned). I ended up changing the fuel and air filters as well as discovering a leak on the #3 fuel injector. At first I figured it was a bad o-ring, but then I noticed that the rear bolt for the rail was broken off and the rail was lifted about 1/4" - just enough for fuel to leak out. So, I will be drilling that out and all getting out the easy out. Found a good replacement bolt in my shop so hopefully it's a quick fix.

 

I still havent figured out the a/c issue, but all else is pretty good. Running on all cylinders, lots of power, and pretty efficient for a 5.4 motor! I took a weekend trip to NC from here in NY to see my daughter graduate HS. About 800 miles round trip and not a single issue.... other than needinding to use the auxiliary 4x60 a/c

Before we left, i changed the upper control arms (they were factory!!) And lower ball joints as well a as the swaybar links. Had it aligned with a set of 10 ply hd 265/70/17 tires a friend scored me for free. Yes, it drives like a truck, but shouldnt it? Haha!

Anyway. I'm still working on the a/c issue and i'm starting to think it is the compressor. There's also and aux a/c unit in the back (driver side across from the sub and amp) i'm wondering if there is a pressure sensor there, or something at all that could make the clutch not enguage.

 

Nope, both the low and high pressure safety switches are under the hood.