AC clutch engaging/disengaging

[Brad]

Recently while driving or idling, the AC clutch engages/disengages every few minutes or so. I also notice when the compressor disengages, it's blowing warm air and when it engages somewhat cold air. I purchased a AC recharging kit that came with the hose/pressure gage from Wal-Mart. The gage, not knowing how accurate it is itself, indicated that I needed no freeon, however, when the clutch disengaged the pressure went up significantly into the red zone. With the engine off, I can easily turn the clutch by hand. I'm really hoping that all I need is a couple more cans of freeon. I had the AC recharged 2-3 yrs. ago at which time the system was tested with no problems. The AC was working great a month ago.
Thanks.

 

[V8BoatBuilder]

The gauge reading is almost meaningless with the system off. When 134a is at ambient temperature, it has a static pressure pretty much irregardless of charge, unless you are VERY low.

It's impossible to accuratley find the proper charge using the low side pressure gauge, for that you need the high side pressure. Buy/rent/borrow/steal a real gauge manifold. Someone posted a link to a $40 set a few days ago.

I redid the A/C on my 97, and the low side pressure was relatively constant between when my vent temps were at 46 degrees and when they were at 40 degrees. At 46 degrees, I still had several ounces of 134 still to add.

http://www.explorerforum.com/forums/showthread.php?s=&threadid=78901 (scroll to the last post)

Your symptoms do appear to indicate a system low on charge. The clutch will cycle normally, but too much cycling is indicative of low 134a. OVERCHARGING IS WORSE THAN UNDERCHARGING

Also check out this thread for general A/C info:
http://www.explorerforum.com/forums/showthread.php?s=&threadid=77331

 

[Brad]

Is it safe to assume that the system is low on freon?
I put only 1 can of freon in seeing that I didn't feel comfortable with the accuracy of the pressure guage that came in the kit, and didn't want to run the risk of overcharging the system. As far as the 1 can helping, I did notice it was a few degrees colder but nothing significantly.

 

[V8BoatBuilder]

The general assumption is that it is low. But you really need that high side pressure value to to be sure.

If you don't want to bother with the high side pressure, here's what I think you should do.
1) Assume your system works, it just has a small leak.
2) Get a digital thermometer and stick it in the center vent. Add the freon on a warm day (75 degrees or higher). You should see the vent temperature cycle with the clutch. It may take time, but it should get down below 45 degrees.
3) Keep the can connected untill vent temps start to rise again, then disconnect. The 134 lost in disconnecting your hoses should bring the temp back down. If not, let off a little.

Worst case, if your high pressure gets to high your cut-off switch will shut down the system.

 

[Brad]

How many cans will it take to fill the system, assuming the freon is very low?
Thanks so much for the info. I do appreciate it.