A/C Problems
 

Okay, I'm no expert on air conditioning systems, but have some basic familiarity. I'm out of ideas and need some help with my A/C (sorry, this is kinda long).

It's a 93 base, converted to R134a. The A/C wasn't working when I bought the car last year due to a big hole in the condensor and one of the aluminum lines (both rubbed against a braided oil line until it wore through). I replaced the condensor and line, and charged the system with one 13oz can of R134a to see if the leaks were fixed. I used a gauge and saw about 35PSI with the compressor running. No leaks, the compressor stayed on constantly at idle, and it blew cold air, so I figured I had it fixed.

Two days later, I turned it on and the compressor was switching on and off about every 10 seconds, though it still blew cold air. I found a slow leak at the top of the dryer, which needed replacement anyways, so I replaced the dryer and o-rings and recharged again, this time using a kit which included 3 12oz cans of R134a and oil (each contained 10oz R134a and 2oz oil). I put in one can, it blew cold air and there were no leaks. Once again, pressure read 35PSI and the compressor stayed on constantly.

So I stop the engine, figuring I was victorious, and let the car cool down for a couple hours. Then I fire it up again and warm it back up, and I turn on the A/C and the compressor is switching on and off about every 10 seconds again, though it's still blowing cold air. I looked the whole system over carefully and found no leaks whatsoever. I checked pressure, and when the compressor is off it's reading about 45PSI, and when it switches on, the pressure drops to a little over 25PSI. I figured maybe it was just low, so I tried adding another can, but the compressor continued to switch on and off, and the pressures did not change much at all.

The R134a conversion label states that the system holds 2LB of refrigerant and 8oz of oil. Figuring maybe it was still low (2 cans = 20oz R134a + 4oz oil), I add the third and final can - the instructions in the kit state that two cans should be enough for most systems, but that some may require a third, so I figure what the heck, it's not working right at this point anyways, and if I can't get it working, I'm just going to yank the whole system out.

Still sitting in the driveway at idle, the compressor still switches on and off, and no significant change in pressures. At this point I give up, and I'm late to be somewhere anyways, so I decide to just drive it as is. I leave the A/C on and get on the road, and as soon as the revs reach about 3K in first (low load), I hear a VERY loud noise from the engine bay that sounds sort of like flatulence crossed with machine gun fire. I back off the throttle, and it goes away. Try it again, same thing happens, so I turn off the A/C. So I guess it's pretty obvious that I overfilled it, so I leave the A/C off until today.

I checked it out today, and there are still no signs of any leaks. I vented out the refrigerant, and recharged it again, this time with just a single 13oz can of regular R134a (no oil that I'm aware of). As is the case every time when I'm charging it from empty, the compressor is staying on constantly, pressure reads about 35PSI constant, and it blows cold air, but I haven't driven it with the A/C on yet. It's sitting cooling off now, and I'll find out shortly when I drive it again whether it will continue to make that noise at 3K, and whether the compressor will switch on and off every 10 seconds.

So here are my questions:

1) Was that loud noise at 3K just violent belt slippage from the compressor locking up under excessive pressure? There don't appear to be any leaks, and the compressor seems to be working now, so I don't think anything blew out/up.

2) Looking at the little window in the line to the dryer, when the A/C is off I see nothing (empty, no fluid visible), and when it's on, I just see a solid whitish foam swirling around in there.

3) Since I can't find anything A/C-related in the FSM, and searching here turned up nothing useful, what is the actual capacity of the system? Is 2LB ridiculous, and the shop that performed the conversion (and filled out that label) were just a bunch of idiots?

4) I know there's a pressure switch in one of the lines to the dryer - does that indicate low pressure, high pressure, or both? In other words, if the compressor is switching on and off every 10 seconds, and the pressure reading appears low (about 25PSI) when the compressor is on, and high (about 45PSI) when the compressor is off, is that switching definitely a result of the pressure switch seeing low pressure? Or could it be something else entirely?

Sorry for all the questions. I know some of you guys are A/C techs/experts, and any pointers you can give me would be greatly appreciated. I'm not looking for an optimized "perfect" system that blows the coldest air possible, I'm just looking to have working A/C that at least blows cooler than ambient. Failing that, I'll just remove the whole thing...

My AC has also been converted and I get a similar problem but my switching seems to be more random than every 10 seconds. Still, it is switching on/off a lot and it gets pretty annoying. It blows cold but not as cold as before the conversion. Hopefully someone has an answer.

Nice to hear from ya bud!
 

DigDug - I'm not A/C expert either. My system will have to be fixed or removed, but other things are a priority first (reliability mods, boost spike, etc). As for #1, don't know, but your guess on the compressor locking up sounds logical.



I thought I remembered reading in one of my Toyota Service Manuals that when the A/C system is turned on, at first you should see a bit of cloudiness, but that should clear after about 2 seconds. After that, it should remain clear when the system is on. That's what I remember, I can go test in on one of my current vehicles with a good A/C. I'll let you know.



Can't help you here either.



On my truck, with a currently good working A/C, the compressor clutch will cycle on and off. I don't necessarily think the cycling on and off means there's a problem. I'm not A/C expert either, but I would suspect since the vehicle is small, the cab is small, that maybe the A/C system capacity might be on the smaller size compared to larger vehicles. Maybe you had the right amount of freon after the 1st can, even though it was cycling the compressor on and off.

I'll let you know about the cloudiness, and in the meantime, I'm going to be learning from your experience here. My "fun times with A/C work," is coming. :D

- JyRO

Section G of the Body Electrical Troubleshooting manual (listed in the stickies) has an excellent diagnostic section on the AC system. (The basic shop manual itself has next to nothing.)

It has a step-by-step procedure to isolate faults, inlcluding the pressure switch.

It sounds to me that your AC thermoswitch may be faulty. This is behind the glovebox. It is the black box on the platform pictured here.

http://smi-web.stanford.edu/people/m...rmoswitch2.JPG

Unfortunately, if it is the problem, you will have to evacuate the entire system to replace it because it requires the removal of the cooling unit. A new thermoswitch is about $60 from Ray.

Interesting - I just read the body electric manual section on the AC system, and it pretty much answers my questions...

Apparently the system is currently low on refrigerant (per the sight glass showing cloudy at all times when the compressor is running). One thing I noticed when I had overfilled it with 3 cans was that the sight glass showed just clear fluid with no bubbles or foam whatsoever, which matches up with the manual stating that this could indicate the proper amount of refrigerant or too much. What's more, when the compressor switched off, the glass showed clear for a moment, then bubbles forming, just as the manual states that the system is overfilled.

So I guess the target is clear fluid with no bubbles when the compressor is on, and bubbles forming and then disappearing immediately when it turns off. It should certainly not appear empty after the compressor turns off, as it does now...

Yet another new and interesting find is that the pressure switch connector has been jumped on my car - the switch isn't even part of the circuit right now, so I guess on the electric side, it must be that thermoswitch (or something mystical happening in the "PCME"). Good call, moconnor!

I'm going to buy one of those manifold gauge sets and check the high-side pressure as well, just to make sure I've got it right. I saw one at Advance yesterday for about $40. I suppose this will also enable me to draw the system to a vacuum before charging it, something I've been meaning to do. I'm sure there's air in there now.

if you did not pull the system down to vac it will have moisture in it. it will eventualy corrode and destroy the compressor. it does cause the sight glass to be cloudy sometimes. only reading the low side pressure when filling a system is not the right or even safe way to do it. also randomly putting oil in the system will also hasten the compressors demise. as will overcharging it. when going to r134 in a r12 system the charge amount will be lower.

at idle ~80 deg f the high side should be ~240 the low ~35

the low side cut out switch usualy will open (disallow voltage to the compressor clutch ) under 20 psi or so

Well, for whatever reason, it's working fine at the moment. Fired the engine up after letting it cool down, switched on the A/C, and the compressor switched on and stayed on constantly at idle. While the sight window still reads cloudy all the time, it's blowing very cold air.

I drove it under varying loads and never heard any noises from the compressor. Even after getting it fully warmed up and driving it a while, the compressor still stays on constantly at idle, and it's nice and cold.

the AC capacity is about 750g, it is in the FSM somewhere - found it last year when i had my AC refilled.

So it's a little over 26 ounces then, correct?

I found this item at Harbor Freight:

http://www.harborfreight.com/cpi/cta...emnumber=92475

It's a compressor-driven vacuum pump for drawing an R134a system to 28" Hg vacuum, and it's pretty cheap at $17. On the other hand, manifold gauges have a third connector for charging/vacuum - anybody used one of these to draw the system to a vacuum? If so, what kind of pump did you use? I'm trying to figure out what exactly I need to evacuate/charge the system correctly.

Also, will drawing the system to a vacuum remove all of the oil? In other words, do I then need to re-add oil before I recharge it? Or will the existing oil still be present?

Clogged System?
 

Mine was doing the same thing just before it completely died just after purchasing the car. I put off having it fixed for a long time. When I finally had it looked at by my rotary specialist, he found the system was clogged with a hard material. He said someone may have put 2 different types of oil in it at some time that were incompatible. I am not an AC expert. Are there different types of oil that can be mixed to cause this problem? If it can happen to my AC it could happen to yours; all I'm saying. Bottom line was I had to replace every single part and line in the system. It works beautifully now. So glad. It's getting hot here in CA.

I don't think there are any mechanical problems with my system, it's just not completely filled (about half), and I don't know how much oil is in there. It still blows very cold though.

As for the oil, R12 systems use a different type, but I don't know why somebody would mix them, unless they just didn't remove all of the old oil when they converted it to R134a. AFAIK, any R134a with oil added will have the correct PAG oil.

My A/C system was open for more than a year, and I had to replace the condensor, dryer, and one of the lines, but now it holds pressure fine with no leaks - as I mentioned above, I even inadvertantly tested it at 150% refrigerant capacity, and still no leaks! Looking at the sight glass, it currently appears cloudy whenever the compressor is on because it's low on refrigerant, but when I had it full (and over-full), it appeared clear just as it should, and cleared up when the compressor shut off just as the FSM prescribes (bubbles form and then clear immediately).

Back to my previous question, anybody know the correct procedure well enough to help me out here? I really need to figure out exactly what tools I need (see my last post), and whether I need to oil it again after evacuating the system. If I can find those details, I'm confident I can get this thing working right.

So far, I know I need a manifold gauge to get both high- and low-side pressures, and a vacuum source to evacuate it (found one at Harbor Freight, see my last post).

Oh, and one more question related to evacuating the system - do you run the compressor while drawing it to a vacuum? Or are you supposed to do that without the compressor running? Obviously you want the compressor running while you're charging it...

specs 3.3 oz in the compressor, 1 in the condenser, 1 in the reciever/drier. (oil)
23.1 oz of r12. when retofitting it will be less. usually by several oz.

you will vac the system with the engine off and the high and low sides connected.

there is no way to remove the oil from the system short of flushing/remoing components and pouring them out. some will go out through any leaks. a small amount will get taken up by the vac, but not much.

you said you have no leaks. how did you decide this???

also if the system was open for a long time you do have a new drier right?

get some syn pag oil. castol makes asome good stuff in a small bottle. concern is that when a system is open for a long time the mineral oil absorbs alot of moisture, this tends to turn into an acidic mixture. obviously not ideal for the components.

if it was open for a considerable time to do it the right way it needs to be flushed and the comp drained.

if you are just going to let it fly i would put 3 oz of pag in the comp and 1.5 in the drier.

charge it up till you see about 200 or so on the high side. bit higher if it is hot (90) or very humid.