Need AC help please

[Vimes]

NOTE: Moved here from the HVAC section, realized I should have put it here.

Hopefully this won't upset anyone that I'm asking this, but I'm kinda stuck. This is on my beater, not my project. 2005 Dodge Dakota, 3.7L engine. The AC went out when the clutch stopped engaging on the compressor. When it would engage it worked great, but the clutch kept slipping more and more until it died, shortly after I bought it.


Anyway, I installed a new compressor, dryer, condenser and all three hoses. The orifice was replaced as it is a nonremovable part of the liquid line. I didn't flush the evaporator since the problem wasn't a clutch failure and not a compressor failure. Vacuumed it down, charged it up, and it showed decent pressure although a little on the low side for R134a. Think it was around 40ish on the low and 200 on the high, at 1500RPM. And, it blew icy cold air.


Now for the problem - The compressor doesn't cycle. It runs constantly. Also, the system is supposed to take 29oz, but I stopped at 41oz, or an extra can, measured on a precision scale before and after adding. The extra can was put in due to the clutch wasn't cycling and the pressure on both the high and low sides wasn't coming up. On past jobs, the compressor would run nonstop while adding, then the clutch would start cycling when the coolant got close to the correct amount. It started blowing R134a out the back of the compressor when I'd rev the engine. Sounds like an angry cat, sprays a fine mist. Am I looking at a bad new compressor or is there something I might have missed here? Possible bad high pressure switch? I know enough about how the AC system works that I've been able to repair them including full replacements over the years but this is the first time I've experienced a failure with new parts and I don't want to throw more parts at it without knowing what I might have screwed up. Thanks.

[NorCal-SS]

Sounds like the high pressure switch may be bad preventing the compressor from cycling off. Which then led to overcharging the system and causing the compressor seal to fail. Just a hunch from the info provided.

[Tim C]

You've got it overcharged if it calls for 29oz and you put in 41. If conditions are right it won't cycle, that's not a good indication that the charge is correct. It's making the noise and spraying the oil/refrigerant mist out the safety pop off valve on the compressor similar to the safety valve on your shop air compressor. Pull out the refrigerant and weigh in the correct amount. New compressor should be fine.

A high pressure switch should cut power to clutch before it hits the safety but not always. Some systems don't have a high pressure cutout either. If you do it could be stuck. Either way it's overcharged, start there.

[Vimes]

OK, will do. I'll report back in a day or three.

[Vimes]

Update - Got the system evacuated, then vacuumed it down. Still holds excellent vacuum. Added 3oz of oil and 29 oz of R134A, with the oil as part of that load since it's an oil and R134a mix. Comes to it I can add 2-3 more ounces. Measured by weighing each can before and after on a precision scale (don't tell the wife). I also replaced the high pressure switch, and there is no low pressure switch. System cools like an icebox now, and I don't get the hissing when I give it gas anymore so at least that part is fixed. Pressures looked good when I was done with about 30 on the low and 225 to 250 on the high, on a 90 degree day, engine at about 1500RPM. However, the clutch still does not cycle. It turns on and off if I hit the AC button on and off and doesn't act like it's seizing, but the compressor is either on or it's off now. There's a light bit of random clatter to it as well, so wondering now if maybe I have a bad new compressor. Sorry, no idea how much oil is in the system now. Any other things I might look at on the failure to cycle?

[KEGS73]

as said above. depending on the vehicle set up the clutch won't cycle until it either builds too much pressure on the high side or too little pressure on the low side. you pressures sound fine. I would pull about an ounce out though. everything im seeing says 28oz is max fill on you system. other than that I would let it go

[Tim C]

Don't worry about the cycling. Pressure looks good, it's cold. Like I said, it may not cycle depending on ambient temp, humidity, pressure, etc. on a cooler morning it may cycle for example. Cycling by itself is absolutely not an indication of a proper working ac system. Enjoy your AC!

[Vimes]

Good deal, thanks all! Mods, go ahead and remove, appreciate it.