AC Clutch Engages/Disengages

I have an interesting problem, that possibly someone can help point me in the right direction.

1997 Ford Explorer

When in DRIVE or REVERSE and with the air conditioner turned on, the AC clutch will engage, then about 1 second later will disengage, another 1 second, re-engage, and so on and so on; in a continiously cycle. The air conditioner does blow cold air, so it is compressing (at lease part if the time it is engaged.) If I put the Explorer in PARK or NEUTRAL the AC clutch engages and stay engaged as is should. As you can imagine, while driving the engine has a difficult time idling properly.

At first, I thought this was an AC clutch problem, but after discovering that it works fine in PARK or NEUTRAL it must be something else. How does the AC system interact with the transmission drive system? Is this a computer glitch? Has anybody seem this behavior before, or know what I can do to repair it?

Thanks in advance for any help.
Robert

You should check the pressure in your AC system. The high side should be between 250 and 300 lbs. If you don't know anyone with the gauges, a simple short hose with the AC gauge can be purchased fairly cheap at many auto supply shops like Pep Boys or Kragen. The high and low fittings are of different size so that gauge can only go on to the correct fitting. It almost sounds like too high a pressure? Did someone recently add to the system?

There is also a sight glass on top of the filter (receiver/drier). Do you see a lot of bubbles while the system is on? Too many bubbles or nothing seen in the sight glass indicates low charge. If the pressure is okay, then the problem could be electrical....but we'll cross that bridge later if we have to.

Thanks for your response.

No, work has been done to the car in over 2 years, thus no AC charges.
I have read another article claiming that if the car is idling too low, it could cause the AC compressor to kick on and off like this. So perhaps a tune-up is in order. I have also read postings about IAC problems, so maybe something to look at there, although the car does not die, just idles rough when the AC kick on and off rapidly.

Thanks,
Robert

Well okay. Then what my mind's eye sees is the possibility of a low charge almost low enough for the low pressure switch to cut the compressor out of the circuit. Do you know what the receiver/driver is and where to find it? It sort of looks like a black cylinder on one of the metal AC lines in the engine compartment. Follow the lines back from the condensor in front of the radiator to find it. At the very top is a sight glass viewing port that is about 1/2 inch wide. Start your engine, turn the AC on, raise the RPM and then look through that sight glass. You'll probably see bubbles flowing by when the compressor is engaged. If that is the case, then your system pressure is too low at idle. Considering that your car is 7 years old, it's just at about the average point in time of needing a charge to top-off the original charge. Why? Because it's normal for a slight seepage to occur at the AC pump seal over a long period of time. This doesn't necessarily mean that you have a defect with your system. Properly charged, the bubbles in the sight glass disappear as the maximum pressure of 250-300 PSI is attained. In fact, if you don't have the gauges but do have the charging hose & valve, you can just add enough Freon 12 or R-134 (whichever your system uses) until the bubbles just disappear. Remember to hold the can upside down to allow the fluid to flow. I hope that your problem is this simple. Give us some feedback if it is.

I know what the AC Drier is, I searched the lines but could not find the glass viewing port. I have seen this on other cars, but did not see it on the explorer.
Starting with the assumption the system had a low-charge in the AC Compressor. After getting a R134A kit I connected it to the low pressure side of the AC system (located near the AC drier). When the AC is turned off, the pressure reads around 80 (which is in the red-overcharge portion of the gauge.) when the AC system is turned ON in the MAX AC mode, it reads around 40. (which is in the full portion of the gauge) So the system appears to already have enough R134A coolant? Right? I went ahead and opened the valve to see if the system would take any more R134a, but it did not seem to take any.

I got another tip info from another forum about the AC compressor will cut off if the engine's rpm is too low. Well, I gave the old Explorer a tune up today. Replaced the spark plugs, air filter, PCV, plug wires, fuel filter, & serpentine belt. (By the way, the spark plug on the passenger side closest to the firewall was a mother to change, it easily took as long to change that one as the other 5 combined.) Now the engine is running much smoother and the AC clutch is not cycling like it was. At lease the is the initial results after about a 15 minute driving test. I'll report back if the problem re-surfaces.

Thank,
Robert

Stupid me, I was looking for the glass view port on the AC line, not directly on the drier, I'll recheck this tommorrow to make sure there are no bubbles.

Thanks,
Robert