A/C Cycling

This problem started last year and I really didn't mess with it. Now that is starting to get hot in the Dallas area it's time to get my A/C going again.

Here's my problem.

The a/c compressor will only come on for about 3 seconds then shuts off. It's not even on long enough for me to get any reading with my gauges. I was going to try to add some Freon but, the compressor will not stay on long enough.

Any help or ideas would be appreciated.


Thanks,

Cody

What year? You profile suggests 2000 but your handle suggests 1990.

You should be able to get a reading without the compressor engaged. High and low pressure ports read the same and should be about the ambient temp.

If it's a 2000, you need to fill it by weight. That means evac first then fill. If you're really that low, you likely have a leak that should be fixed first.

Sorry I guess I should have said that it's on my 2000.

Thanks for the info so far.

I actually have the same thing going on with my wifes Cherokee. The AC wasn't getting cool so I snagged a bottle of refrigerant to refill it. At first the compressor wouldn't come on so I added some freon and it started to engage. But like the OP, it will engage for 5 seconds or so, turn off for 5 to 10 seconds, then come back on, etc. The question I have is: on the can of refrigerant it says that the pressure reading (on the low side where you hook the bottle up) should be taking while the compressor is running. When it isn't running the pressure reads around 270 psi (IIRC) which is right on the boundary of being overfilled on the gauge. However, when the compressor IS running it is only reading about 20 psi which is way low. I'm thinking that I should continue to fill until it is in the green on the gauge when the compressor IS running, but don't want to over fill. Any AC experts out there know if this is the case? I don't want to guess and blow up the wifes DD!

As a side note, after adding the small amount that I did to get the compressor to engage the AC is now starting to feel cooler, but not as cool as it has been in the past.

OK. the Heep need to be seen by a professional AC guy if it will need to be drained then refilled.

Short cycling (what you have going on here) is usually assignable to the refrigerant pressure being either too low or too high. The only way to ensure the proper fill is to pump it out then, evacuate the system with a vacuum pump, and refill. There are two pressure sensors in the system that apply. The Low and the High Pressure sensors. To verify those will take the installation of gauges onto the system to monitor. Also, a professional thing.

So, you see, just adding more refrigerant can compound the issue at hand. The 97 I had started short cycling and it turned out to be the high side sensor going bad. The PCM thought the system was over pressured so it shut it down.

Just saying here the best/fastest method is a good shop. Check with your local BBB to get a name of a shop unless you have experience with one already.

There are only three things in the a/c system that tell the mechanical system to run. A high and low pressure switch, and the clutch.
To rule out a flaky clutch get a test light and make sure its getting a steady signal. Also get a real set of hi/lo gauges and turn it on and see what it is doing. if the system is just cycling on/off and the pressure isnt shooting down to less than 15 and the high side isnt creeping passed 350 +/- then your charge should be good. You could jump either connector for the sensors to see which one is causing trouble.

But, if your gonna spend the cash on gauges, Freon etc, you might as well just take it to a shop and have them vacuum, and recharge it most shops will do it for ~80$ and if the find the problem you could handle it or they can. Changing the sensors doesn't cause a loss of pressure because they are both on shrader valves.

^^What he said.

By the time you roll up the bucks into the equipment needed to do the one job, a profesional would have it done for less. Pressure checks are sometimes dome for nearly free at most shops...

Since I did not get an answer to my question I will post it myself. The answer is yes, when you are using the recharging cans that have a gauge your pressure reading should be taken when the compressor is running. After initially adding approximately half the can the compressor was doing the cycling I initially described. A quick google and I had my answer. So I hooked the can back up, started adding the second half of the refridgerant, and sure enough the compressor began running constantly. As I emptied the second half of the can into the system the gauge reading moved up into the "green", I forget the psi off the top of my head, but now the AC is working great and about freezes you out when it is on max. Just for kicks and giggles I went and bought an AC dual gauge set up and it confirmed that the system was charged within specs.

Thank you, drive through please.

Glad you got it fixed. You could have easily overcharged it with a normal low side reading if the orifice tube or expansion valve was partially blocked. You really need that high side reading as well. Charging by weight is your most foolproof way.