On my 96 Explorer 4.0L X code, 4WD the A/C clutch just keeps cycling every few seconds. He just bought it and the previous owner never checked it out, but thinks it needed recharge. We bought a can of 134A with a squeeze trigger and a gauge made into it. When connected to the low side port it stays within the full range, but everytime the clutch cycles it fluctuates within that range. So what could be wrong with it? The compressor isn't any more noisy than my Ranger's A/C compressor with 199,000 miles on it, and it works great. So is it a bad A/C cycling switch on the accumulator? That's easy to change isn't it? I read the service guide for a 98 Explorer, which I assume is still using the same setup, and it says the switch can be replaced without discharging the system. Is that true on a 96?

 

Sounds liek the switch is doing its job.
You really need to have gauges on both the high and low side to diagnose. Your description could indicate and undercharge. Could also be the Expansion tube is clogging up. This will cause the pressure to hold because the the expansion tube will not flow as needed. I just worked a 96 that was one owner wit the AC never worked on that had almost 1/2 of the tube filter blocked. A gauge on the high side is needed to know if you should add more Freon or repair something.

Low Freon is likely given the age adn the ability of R143A to "leak" thru the hoses.

 

when you read your gauges you need to have it with the compressor on, the pressures with the compressor off are not what you want to be looking at (if I recall correctly with the compressor off the low side will read higher than with the system operating)... you also want to do it slightly above idle (1500RPM). I think that you will find that you need to add some R134a to the system. However, be careful not to overcharge the system as it will also cause problems.

 

The engine should be at 2000 rpm when checking pressures. With the AC off the low sode will balance with the high. Usually about 110 psi. the low side should read around 35psi when the comp is running. The High side could be from 170 to 270. All depends on the air flow over the condensor, the humidity, temp of the car and temp of the day. Put a fan blowing on the from of the car when checking the AC.

The switch cannot be changed without discharging. It reads system pressure, so is tied in to it.

 

I thought too that it was low on freon. But it was at the specified pressure for a full charge on the low side, but it just fluctuated when the compressor kept cycling. But the gauge needle never went about the blue bar on the gauge indicating and overcharge or low charge. It never even dropped below the blue bar on the gauge when it was flucuating down. I read a A/C manual, and the symptoms pointed towards the cycling switch. It wouldn't even taken any freon, probably because it had a full charge. I'll hook a A/C manifold gauge set to it this week and see what's goin on. The gauge was on the can tapper so it only showed low side pressure. I was told some systems usually won't take in anymore freon if the system is fully charged.

 

I don't mean any offense, but you really need to learn a little bit about AC systems before you try to fix yours. You could damage the system, or yourself if you just randomly try to add refrigerant. Many people get lucky and a top off is all that's needed, but those that don't get lucky have to contend with system damage or injury. Often both. Before you do anything else, check out one of the online AC forums and get a feel for what you are doing. I recommend www.autoacforum.com .

<rant>That cheap low side gauge is of very little use. It's a gimmick designed to make it look easy and make money for the producer (Interdynamics). Those cans also contain "snake oil" additives that give you no benefit and can damage your system.

<rant off=""> The system will not stop taking refrigerant when it is fully charged. If the compressor is not running, it will stop taking refrigerant when the pressure in the can and the system are equal. If the compressor is running, it will also take refrigerant until the pressure equalizes, but by then you are way overcharged.

That gauge will only tell you anything when the compressor is running. The low side should read ~30psi while operating. You will need to bypass the cycling switch on the accumulator to take the reading.
As long as the high side isn't blocked, this is ok. If it is blocked, damage can result. This is why you need to see both pressures.

It's hard to resisit all of those brightly colored cans of magic at the parts store that tend to say "Just add this and your system will work like new!!" but in very very fine print say "only use this product if you know what you are doing"
To even think about repairing your AC correctly, some tools are mandatory. The #1 needed tool is a manifold gauge set. Harbor Freight has a decent set for about $40. The #2 tool is a vacuum pump for removing moisture and air before charging. They are $200 or more. You can often rent one from a parts store like AutoZone.
AC repair isn't hard, but there are no quick fixes. Shortcuts usually lead to problems that cost more later.

Good Luck

</rant></rant>

 

I have never seen an A/C system in a car that didn't cycle alot. If there is a load on the system and it is warm outside it will not cycle as much. If the car is cool then it will cycle alot. It will also cycle alot on a hot day once the car is cooled off and the load has been taken away from it. You really can't compare one car to another as far as cycling either. The designs are different and the load that they have are designed different. A simple way to check it is put a small probe type thermometer in the vent, turn the A/C on full cool and run the idle up to about 1500 to 2000 rpm and see what kind of air it puts out.
I agree with Isrx101, if you overcharge the system you can damage it or injure yourself. If you are sure that it needs some refrigerent take the time to get the proper guages and check it correctly. If you overcharge you can also take away cooling just as if it is undercharged. The correct amount is pretty critical to get it perform correctly and do the job right.

 

I know I don't know enough about A/C systems to do major system repairs for this guy. But I've tried to read as many A/C books I could find, and do whatever repair work I can to the A/C system. It's just difficult to remember all the different types of systems and problems they present. I've got an old Datsun B210, that came with aftermarket A/C originally. I tried to redo the entire system. I bought a manifold gauge set, a cheap vacuum pump, and replaced everything in the system by the book. I got it to work, but not efficiently enough for the Georgia heat. It only cools to about 50 when it's about 85 outside. I'm sure there was still moisture in the system even after evacuating 45 mins. Plus it was just a cheap air pump from Harbor tool. It doesn't leak though, it's still holding the charge. It's a simpler system, an expansion valve system. On the Explorer I assumed the compressor was cycling soo frequently because it was low on charge, due to a possible leak. So that's why I tried to install a can with the trigger gauge. And noticed that it wouldn't take. I haven't hooked up my manifold gauges to get both pressures yet. I was looking through the A/C repair guide I had and it said, to bypass the clutch cycling switch and see if the system works and if it does, then the cycling switch is bad. I told this guy I would look at his A/C system and if it's something simple, which in an A/C system I know it never is for a home mechanic, then I will try to help repair it. I want to learn even more about A/C repair, because it's my favorite area of automotive repair, and there's a lot of mechanics that have shops that still don't know all there is to know about A/C work.

 

You probably already know this... but just in case. That B210, is that aftermarket A/C new... i.e. is it running R143a and have the fittings for that? Or is it an older R12 (Freon) system? If your gauges are for the R12 system you will need to get a new set or find adapters to be able to use them on the R134a system.

As a second thought on the 210... if you "updated" the system to run on 134a instead of R12 but the system was originally designed for R12 it will not cool as much as an R134a only system...

 

Good advise by all here, and your desire for knowledge is a good thing. The researching is a good start, but it sounds like next you need to find someone with some knowledge who can give you some apprentice type guidance on how AC systems behave.

The safety concerns mentioned here are very real. Be aware the high side can easily see over 500 psi in situations. Injuries WILL occur if a hose breaks at that pressure.

(K2JJB posted while I was typing with a very good point as well)
On your Datsun, the moisture or air contamination is most likely correct. 45 mins is a bit short to pull down a system. Especially with a weak vac pump. Time is your friend with pumping. The military specs a 24hr draw on vital systems. Of course the real world is usually bit shorter and there are tricks to assist pulling moisture out.

Curious why if you have gauges that you have not hooked them up.
Good Luck and be safe...

 

You've got a good start with the gauges. Now you just need to use them and learn how to interpret the readings. If your vacuum pump is a venturi type that uses compressed air, you're right, it just won't cut it. The best deal I've ever found on a vacuum pump for DIY is at www.ackits.com. Go to the vacuum pump page and look at the second one ($135).
MVAC was my favorite area too. I've been out of the automotive field for a few years, but I still do MVAC in my own shop. Being a bit of a masochist, I also enjoy doing electrical work on vehicles.
If you really want to learn more, start hanging out at www.autoacforum.com A lot of the guys there are MVAC pros who want to help DIYers like yourself learn more about it.
You're right about shops that don't know about AC work. I do the MVAC for 3 well respected shops in my area. Many folks are intimidated by it.

So hook up your gauges to the truck (fan on high, MAX AC, doors open, 1500RPM) and check the pressures and see how fast it cycles. It's probably low on refrigerant, but this will verify it. Post back with the results.