My 06 Pacifica A/C compressor is not staying on long enough to make the air cold when it cycles. It will come on and stay on for a few seconds to 25 seconds and shuts off. It differs all the time but probably averages about 3 or 4 seconds and stops. It may stay on for 3 seconds and shut off for 20. Most of the time when I really need it, it will cycle for a few seconds and and shut off for 5 to 10 seconds and keep going like that. Won't stay on for more than a few seconds. When it does stay on, the air gets cold, but it never stays on long enough. It seems to work better (stay's on longer) when the outside temp is 70 to 75. The air will get cold but still not as cold as it should be. When it's much warmer (80 to 90), it gets worse, won't stay on for more than 3 seconds. I already replaced the pressure transducer on the high pressure line. No help. The system shows that the charge is good with the usual auto store bought gauges on the low pressure line.
I have a friend who has an auto repair shop and he told me that the system could still be low on refridgerant even though my gauge say's that it's fully charged. He say's he's seen systems show a full charge but when refridgerant was evacuated and weighed, it was very low. Have any of you A/C guy's out there ever heard of a situation like this??
Last summer my A/C worked great until the end of summer when it started to act up like this. Last fall, my compressor clutch fell apart (I believe due to the constant on-off cycles) and I replaced the clutch without opening the system. Now that it's getting hot, I need to get to the bottom of this problem before I melt another clutch.
I'm thinking that my friend may be right because of the way it operates in different temps. Could the system have a better charge when it's cooler outside causing the compressor to cycle longer than it does when it's hot outside?? I know that refridgerant is temperature sensitive but I'm baffled. Anyone ever see this before?? Any help is greatly appreciated! Thanks.........Dave

 

Hi,
no expert, but your symptoms in my experience have typically been related to low freon. The static pressure is high enough to achieve compressor cut-in, but once running the low pressure side drops very quickly below the cut-out level and the cycle repeats itself. I have more experience with Ford A/C and I remember a chart in my Windstar shop manual that showed normal cycling times at various temperatures. For an otherwise normal system, at about 85-90 degrees, the cycling time curve went infinite. In other words at that temperature I could expect the system to run continuously. And it did.

Hope you get it worked out. Hot stinks.

 

Yes, hot does stink! Thats what my buddy thinks and it does make sense, but why does the guage show a full charge on the low side?? I've already wasted $60 for the pressure transducer. I'll have to take another shot in the dark having the system drained to see how much refridgerant is in the system. I guess if I take enough shots, I'm bound to hit something sooner or later! I'd like to know if anyone's ever seen a guage show a good charge when there really isn't. I used 2 different guages that both read the same. Can there be a sufficient amount of pressure on the low side to show a full charge on a guage when the system is low on refridgerant?? My compressor seemed to stay on for longer periods when the air temperature outside was around 70. When it get's above 85, it won't cycle for more than a couple seconds. Would a low freon level act like this or the opposite??

 

Again I am not a trained tech. But your gauges like mine, only measure pressure not quantity or mass. Your A/C system, if it has enough freon in it to allow it to run - pressure transducer senses appropriate pressure - will produce a low side indication that is fairly normal even when low on freon (I assume what you are actually seeing is the pressure drop while the compressor runs, slowly increase when it cuts out, then drop again etc.)

I don't know exactly what a shop would do first, but my inclination is that they would attach their gear - low and high side guages and see what BOTH were doing. After that I'm thinking most would add 1/2 to 1 Lb. of 134a to see if the system improved - low/high side pressures and output temp at the A/C registers in the car. I could be full of it because they may be constrained to have to evacuate and leak test the system before being able to add any freon - EPA at your service.

So, that leaves you with the choice to add your own freon or take the car to your friend or another shop for evaluation. If you add - your system is sensitive to proper freon charge so too much or too little is problematic. When I add freon I use a digital kitchen scale and weigh the can WITH the hose before adding. I then get the system running, open the valve to add freon and let it run while holding the suction line to see if it is getting colder. If so, I will add until the line is fairly cold - slow process so I will guess 3-4 min. Then I will stop, disconnect and re-weigh the can and hose. Most of my cars have had a capacity around 2 pounds so I am very suspicious of adding more than 1. I actually go in about 4 ounce shots if possible stopping at the least amount that brings the system back to a fairly normal state - low and high side pressure in normal range, low pressure line same temperature (by feel) in and out of the firewall, and normal register temperature (varies by outside temp but I usually see something south of 50).

So take that all for what you will. If Djinn or any of the other pro's disagree with what I have written LISTEN TO THEM.

Again good luck with it. And BTW nice job on the clutch change. I am impressed that with the design of the Pac. the job can be done on the car and with the system closed. I have had more clutch failures than any other A/C component.

 

What No-One seems to realize, Is there is an entirely seperate half of your A/C system. Its called the Head side, or High Side of the system......

Is the freon low, and the low side switch cycles the compressor...or.... Is the Head side to high and cycles the compressor..???

The little "Free Gauge With Purchase" tool that you get with the charging kit...only does low side readings.....And ONLY if the car is running and the compressor on steady..can you trust what it says.... Even Then...Without the other half of the readings, The information you have from a low side gauge alone is useless.

 

Well thanks guy's for your replies. I have a decent gauge, but it is only for the low side. It's not a freebie that came with a can of freon. From what my manual say's, the compressor is cycled on by 2 sensors. One is the transducer on the high line and the other is a sensor on the evaporator I think it was. It's somewhere on the A/C heater housing under the dash.
My friend said the best thing to do would be to evacuate the system and weigh the freon, compare to specs. At this point, I think thats probably a good idea. If it doesn't fix the problem, at least I'll know that the system has a sufficient amount of freon and the problem must be elsewhere.
I'll tell you, the clutch wasn't the easiest thing I've ever done. After removing the wheel well shroud, there is barely enough room to get at the clutch once you remove the 4 mounting bolts on the compressor and pull the front of it down as far as it'll go which is about 2 inches. It'll drop down just enough to get at it. I had the car on ramps in my driveway, so I was on my back the whole time. The hardest part for me was loosening the bolt in the middle of the clutch pulley. I didn't think to try to do that before taking the serpintine belt off, and I don't even know if I could get at it with the belt on and compressor bolted in place. Anyway, it saved me some money. Now that I've done it, I'll do it again if I ever need to. It really wasn't as bad as I thought it would be. Hopefully that'll never happen. Thanks again for your thoughts guy's. I'll let you know what happens........Dave

 

I know this is a pretty old thread, but maybe somebody searching the web will stumble onto this. My 08 pacifica was doing same behavior as above. The low pressure side was reading fine, but the clutch would only come on or a few seconds, or not at all. For better or worse, I used an old GM servicing trick - and that is to pull the AC compressor clutch relay (its in the fuse/relay box in the engine compartment) and jumpered pin-holes 30 to pin 87 with a paper clip (you can read the pin numbers on the bottom of the relay). This forces the clutch compressor on with the engine running - My system took a full can 13oz can of R134A refrigerant, and the pressure gage is reading in the GOOD range now with the engine running and the compressor engaged. Better yet, it gets icebox cold in the car now. Obviously, there's a leak in the system somewhere, but hopefully its very small and very low, and that 13 oz can will last a whole season or multiple seasons - only time will tell.

 

Also, the low pressure port on the 2008 with the 4.0L engine is hard to get to - I had to pull over the plastic engine cover, and reach into a tight gap along the firewall to get down to the low pressure port - what engineer designed that??? (by the way, I'm an engineer, I can be mad at other engineers)