A/C Off and On

Well for months our A/C had worked for 20min then quit. Turn the A/C off and on every 1 min 4-19 times and it will start working again. Last night I pulled into the garage and it was working so I stuck the guage on it. It ran from 24-30psi while blowing cold (not very cold, but good). It stayed on......go figure. So I turned it off (back up to 100psi - ambient temp) then turned the A/C back on....the compressor kicks on, but the A/C doesn't blow cold...then it did it!!! I heard something like a switch click and the pressure dropped to 30psi and the cold air started.

What is making it not work?

kind of simple but check your coolant level mine was doing the same exact thing i filled the coolant up and it stopped

coolant for radiator, or refrigerant r-134?

could it be the high pressure switch?

Are you absolutely sure the compressor was engaged and turning when it was blowing warm *before* you heard the click? Then once you heard it, it started blowing cold?

Yes. When I turn the setting to A/C, I hear the compressor engage and the rpms dip. When looking at it, it is engaged and spinning. So it will spin/engage without blowing cold air all the time. I am just trying to figure out what the click was that all of a sudden allowed it to drop the pressure on the low side and start blowing cold. Sounded like some sort of switch.

Any kind of switch associated with the compressor (low pressure cutoff, high pressure cutoff, ac relay, ac controls) is used to engage/disengage the clutch.

Sounds like you have enough refrigerant to cool things off when it's working although it appear to be a bit on the low side. You might try have the system evacuated then charged.

Can you tell where the "click" comes from? Is it in the engine compartment, the PDC, or under the dash?

The click came from the engine department. Is it possible that the compressor is spinning but not engaged? At one point a few months ago someone had me convinced that I needed to take out a shim or two from the compressor clutch. In other words, the compressor is engaging, but the engagment might not be active inside the compressor. Does that make sense?

That's why I asked if you were sure the clutch was spinning. If the air gap is off, you'll get the relay to click and the system will "think" it's on (power applied to clutch), but the clutch may not engage. This will be obvious looking at the clutch. Usually happens once the engine gets hot.

I would go back and double check. Have a friend turn the AC on and off while you observe the clutch action. Removing a shim is fairly easy to do and you don't have to discharge the system. If you search on air gap, you'll find plenty of hits.

No, the clutch is actually spinning. That is the first thing I check. What I frear is that the clutch is engaged/spinning and that somthing between the spinning clutch and the compressor (the shims) are getting in the way of parts inside the compressor actually spinning. But the click sound made me think it was some kind of switch kicking on unrelated to the clutch.

Well, try this.

There's a wire coming out of the clutch that connects to a quick disconnect terminal. Disconnect it. With the engine running, fan on high, and your gages on the fittings, connect a jumper from the + battery terminal to the lead running to the compressor. This will apply 12v directly to the clutch, bypassing everything else. As soon as you connect it, the clutch should engage and start blowing cold air (may take a minute or so to get cold). You should see the pressures change as well. Don't run like this too long, just long enough to verify it's cold. Disconnect and wait for the pressures to normalize and feel warm air out the vents. Jump the compressor again. Do this several times to verify the clutch works and when it does, you get cold air.

While doing this, observe the line pressures as well. If the low side drops below ~20 psi, disconnect it.

No AC in mine either. Here is how it stands:
Low coolant pressure ('bout near zero)
12v not present at clutch when AC turned on
Compressor turns freely

It all started when I tried to charge the system with coolant and it wouldn't accept any. I found that the when engaging the AC the clutch wasn't kicking in. I applied 12v directly to the clutch and it kicked in immediately so I believe the switch wasn't sending the power (due to low coolant pressure) to engage it. After bypassing in the 12v, the system still wouldn't accept any coolant. Does that sound like the clutch is slipping and not turning the compressor? Seems to me that if the compressor doesn't spin then it wouldn't take in any coolant, which in turn wouldn't allow the pressure to build up enough to make the low pressure switch, which wouldn't send the necessary 12v to engage the clutch. Does that make any sense? I may check the air gap tonight to see if that is the case but am just looking for a little confirmation in my troubleshooting.

I did have the AC system working pretty efficiently about 3 years ago (father-in-law's Jeep) but he recently passed it down to me and am just trying to get some of the little things working again on it. Thanks for any tips.

'87 Cherokee Chief, 4.0, AW4, all stock aside from a 2" spacer/shackle lift.

Refrigerant, not coolant. Several questions here, but to start, did you open the service valve on the compressor when ready to charge? This is usually the problem when the system accepts absolutely no refrigerant. And, of course, your gauge will show zero pressure.

My bad...I meant refrigerant. Nope, I didn't open a service valve on the compressor at all. I'll look at that tonight as well - it didn't accept the slightest bit of refrigerant so that definitely could be a piece of the puzzle. I downloaded the compressor/clutch maintenance .pdf file linked in another thread too so that may help with troubleshooting further. Thanks for the advice.

The valve opens with a clockwise rotation and you want to open it just enough to allow the flow of refrigerant, usually about a half to one turn (too far and it cuts off refrigerant flow internally). The refrigerant container will get cold and the gauge will indicate that something is happening, which is about all the single ended gauges that come with recharge kits are useful for. Probably obvious, but you need to close the valve counter-clockwise before removing the quick-disconnect fitting from the port.

I have always ended up using vise-grips to turn the valve stems.

I have never had to jump the low pressure switch to start the compressor in order to charge the system, even after a professional evacuation prior to a 134a conversion on my '85, but I don't know if this is just the result of dumb luck of the truly clueless.

I relate this to get you started and perhaps provide some data for a further evaluation. Anything more and you will want to follow the advice of Saudade who actually knows what he is talking about.

I've charged my '98 civic, '03 TJ and my father-in-law's "new" '01 XJ without having to open a valve on the compressor. I'm hoping this is just a change from the older models to the newer ones. I'm using a single-gauge hose kit and swapping in new bottles like you said. I know it didn't take a bit of refrigerant since the bottle stayed full (and warm), the pressure didn't spike nor drop, and the lines stayed dry and warm. I have never needed to jump the wire to the clutch before either - but I did it just as a way of seeing if the thing was even working. I'll look closer at the fuses and such too, but figure that I have more problems than just a wiring one if I couldn't even get it to take refrigerant once jumpered!
Thanks again....I appreciate the insight.

Yes, this applies to older models--they did away with the service valves around '96 or so.