A couple months ago I had a battery failure in my 04 V8 Explorer – Eddie Bowser– on the road. The message panel went nuts with obscure nonsensical messages and codes a few of which I captured with my phone at great peril to myself and others. I got home, but on shutdown the battery was stone cold dead. The pos term was all corroded but I jumped it and took it to a parts store and bought a battery putting it in at the parking lot. I cleaned the term as best I could vowing to do a better job at home. All was fine.

A week or two later on leaving work the AC didn’t work all the way home nor the next day. Then one more day later it was working again. A week after that it was off again and then as before a day or two later on again. The clutch wasn’t engaging. During a off time I checked equalized pressure. It was 95psi. I didn’t check the temp but expect it was about 85. It was off again this weekend so I thought I would dig a bit deeper.

I changed the low side cutoff switch – nothing. Like a forum poster here I swapped the AC Clutch Relay with the one next to it – same part – nothing. I took a moment to clean the pos terminal which shut down the computer and I wiggled the wiring connection at the clutch in a failed attempt to get it off. After all this I started it up and the clutch engaged!

I immediately put the gauges on it:

· Outside temp 71-72, AC temp set to dual 60s, Fanfull, Recirc on, Engine at 750+- idle.

· Clutch cycles on for 30 sec drawing down the lowside to 22-23 and the high side builds to 148-150.

· Clutch cycles off for 10 sec low side builds to 40 and high drops to 100 before it cycles on again.

· Temp from two center ducts: pass side 45-48, drvside 52 – 55.

· On shutdown pressure equalizes to 80.

My questions are:

1. What is the low cutoff switches’ designed cutoff pressure?

2. Is there anything unusual in the described system operation above?

3. Why the different duct temps?

4. Are these sequences of events just coincidental?

5. What’s with the clutch, man?

I don’t think I did anything of any consequence. It may be off again in a week.

 

I suspect that being an 04, you may be just a little low on charge (time seepage thru connections and compressor shaft seal) . Your equalized static pressure reading of 95psi at 85° is correct. However, at 71-71° ambient temperature, you should be reading about 35-40 psi on the low side and 145-160 psi on the high side when the compressor is engaged. Since you're only reading 22-23 low side and 148-150 high side is where it leads me to believe your just low enough to cause the cycling. With your low side pressure, the low pressure switch is causing the compressor to disengage to keep the evaporator from freezing. Since the ambient and under hood temps affect the system pressures, I would evacuate the system and put a full charge back in before replacing parts. As far as the temp difference between the drivers and passenger side vent reading, I would suspect that is caused by the way the multiple blend doors operate. I have the same issue with my 04 Freestar with the passenger side being colder then the drivers.

 

So, higher RPMs won't raise the pressures and stop the cycling?

 

Higher RPMs will raise the high side pressure to a point. But if you're low on charge, the low side pressure will remain low causing the clutch to disengage. You can't pump what you don't have. What pressures do you have when running the engine at 1500 RPM and a box fan set in front of the radiator set on the high position?

 

Thank you for your informative post guys!

 

Thanks for the reply and good advice. It probably is low but that doesn't explain why the compressor clutch doesn't engage at all sometimes - not even when I jump the pressure switch. On initial start it should come on until it draws down the low side to below the 20 or 22 lbs. After all, at start the low side at 80 to 100 lbs - same as the high. In fact under this circumstance there is no power to the pressure switch. What controls power to the pressure switch and why would it be intermittent?

Good thing it's winter now,

Rock

 

This won't help, but unfortunately, being a 2004 the computer controls your A/C system. Just jumping out the low pressure switch won't do it like the older systems with an On/Off switch that just applies 12vdc thru the low and high pressure switches to the compressor. When you turn the A/C on, the computer goes out and scans all associated components such as the low pressure switch, high pressure switch, A/C fan(s), coolant temp, evaporator temp, ambient temp and so on before applying the required voltage to the system components. If the computer sees something it shouldn't or doesn't see something it should, then no A/C activation.

You'll most likely need a wiring diagram along with a shop manual troubleshooting chart for your Explorer to follow the system thru.

 

It's off again now. I will reset the computer with a battery disconnect to see if the clutch comes on again like the last time. Given my story about the battery above I could have fried my computer.