slow_90firebird

Alright, I need some advise from all you A/C guys out there.

Since the spring, I have been on a quest to get my A/C working, without converting refridgerants. Mostly because I read the R-12 is supposed to blow ice cold in these cars, and because I didnt want to replace parts to do a 134a conversion.

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Ever since I got the car, if you turned on the A/C, the compressor would come on for a split second, go off for a few seconds, and then come back on. Static pressure was ~60psi on the low side.

I came across some R-12, in cans. I had an R-12 can tap and hose from autozone too. First one I put in was a 14oz leak finder, using red dye that looks like blood. After putting the whole can in, the compressor would stay on for maybe 10-15 seconds straight, off for a split second, then back on for another stretch. Mildly cool air at the vents.

Then I added a 12oz can of new R-12 from napa. After maybe 1/4 of that can was in, the compressor stayed on. I had to put the whole thing in though, because it uses the piercing stem to tap the can. Now I was getting cool (55* F) vent temps on MAX, compressor stays on.

I figured I over charged it a little, so I checked it with the guages. Low side was at 55psi at idle, max cool. I *whispers* let some out to get the low side down to 30psi. Warm day, 80* and humid. I cant get a high side reading because the fitting is wrong!

Now with the low side at 30psi, the temps are the same, if not a littler warmer, than when it was at 55psi. Also, even though the compressor stays on 100% still, I dont get ice or much condensation on the cold lines like I did with the full 2 cans in there.

So what do you guys think?? My goal was to try to get like 30* vent temps or close to it. Somebody I know used to have r-12 in an older car too, and on a really humid day, he made it snow inside the car LOL.

Reid Fleming

iTrader: (2)

Are both fans coming on when the A/C is on? Have you tried going for a drive and measuring the temps? It will be colder when you're moving (getting air flow across the condenser)

slow_90firebird

1) only a single fan. Its an LO3 car, I think only the TPI cars got dual fans.

2) It does get slightly colder when driving, but not by much.

there has gotta be something else I am missing, but I really need new hoses for my guage manifold, and that GM adapter for the high side.

slow_90firebird

just measured again. its 82* outside now, 70% humidity.

The vent temp never got below 64* and the ambinet interior temp stayed at 80*, and this was a decent length drive at 55-60mph on the state roads.

black89ws6

On a system the size of our thirdgen's, when the compressor comes on only for a second, before cycling, the system (probably) has only about a 6-10 oz of R12 left. This is on a system that should have 36 oz for a full charge.

Early model thirdgens, (with the exact same ac system components as later models), were labeled for 3.00 lbs, while later models were labeled for 2.25 lbs. Back in the day, they just charged them a little extra, to allow a small leakage reserve. Point is, with R12, 2.25 lbs is the ideal charge...but an overcharge that is still less then 3.00lbs total, should still run decent.

The 14 oz can you used probably had 12 oz R12, and 2 oz of oil/leak detector/o-ring additive. By my figures, you put in 24 oz refrigerant. With the estimated 6-10oz that were likely in it already, you likely had 30-34 oz. It is not likely you were overcharged.

When you run the blower on high, with the engine at idle, that representative of your ac system at minimum output, under maximum load. You have the right idea, in that you do get the better cooling at lower pressure, but even a tip-top condition system on these cars will struggle to pull down to 30 idling with blower on high. Especially one with only a single fan.

Here's what you've probably got so far:
1) Probably undercharged. You were probably a hair low already when you decided to vent some. It's difficult to say where you are now, as there's no decent way of estimating how much you vented. You probably need at least another can.

2) Have you even looked at your condenser? It needs to be in good shape before you charge any more refrigerant. Chances are, it is dirty, or has bent fins, or both. If it's dirty, take loose the upper radiator mounts, lean the radiator back to get access to the condenser, and hit it hard with a garden hose. If the fins are bent, straighten them with a a small thin, non-pointy flat edge, like a butterknife. This is a tedious chore, that really sucks, but if you want it to cool, the condenser needs airflow.

3) You probably have a leak somewhere. hopefully, it is very small. Look at both connections at the condenser, both lines at the back of the compressor, and the connections near the firewall for the accumulator and evaporator. If any of them are oily/greasy, they are probably the guilty connection. Also look at the front of the compressor clutch. If it is greasy, the compressor shaft seal is probably leaking (although sometimes these can seep just a tiny bit of reefer oil without leaking refrigerant, so greasy here is not automatically bad).

I can give you a workaround for not having a high side pressure reading. Keep in mind, throughout a refrigeration system, temperature and pressure are directly related. If you can't get a pressure, get a temperature. Get an instant read meat thermometer (digital is best). Cut a 2 inch circle out of cardboard. Stick the thermometer through that circle, then GENTLY! stick the thermometer into the condenser, as near to the middle as possible. Push the cardboard circle up against the condenser, to minimize airflow around the thermometer tip. On a good, hot day, engine idling, blower on high, this should be 40-50 degrees above ambient temp. If you find a PT chart, like this one, you can determine the pressure, from the temperature reading you got.

slow_90firebird

I will have to look into getting another can of freon then...

Also, I will look at the condensor. I dont think it will be too bad, though, because the car is pretty clean and still relatively low milage.

If 30 psi is too low, what should I look for on the low side then? The reason I thought that I might still have too much refridgerant left in there, is because the compressor stays on 100% of the time. The guy I work with told me even on R-12 systems, the compressor should cycle on and off with the proper charge. Like the new cars do with 134, its on for a minute, then off for a minute, then on again...

On my car, when it was low, it cycled on an off, but never stayed on for more than a split second. And it was off for like 5-10 seconds. After the first can of leak dye, it stayed predominately on, but would cycle off (for a split second) then go back on. I have yet to see it spend even amounts of time on and off, like it should.

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Another hint of info:

Before I even barely touched it, when it still had the low factory charge, the static (engine off) pressure on the low side was like 60-70 psi.

Also, the guy at work said I should check the "orfice tube" or something. But I cant find where / what that is. He said on the older cars they get clogged and cause it to blow cool but not cold. However, I wouldnt want to open the A/C lines to check this thing. Then I would have to vent all the freon, and also get moisture in the system!

Reid Fleming

iTrader: (2)

When I had 1.9 lbs of R-12 in my car, it would cycle like crazy. Like jerking you back and forth going down the highway. My car calls for 2.25 lbs of R-12. So you've gotta be juuuuust right.

With a properly filled system, whether it cycles or not is hard to say. Stopped in traffic, it may run constantly. On the highway it may cycle on and off more often. Running the fan on low speed, it is more likely to cycle than it is with the fan on high speed. (slower air means the coil gets colder)

At 80°/70% humidity, your compressor will be on most of the time. That's a lot of humidity to have to condense the heat out into.

Yes the orifice tube is a good idea to change out. When compressors blow up, those things get plugged up in grime.

If you're getting 64° out the ducts and the compressor is on constantly, it sounds like you have too much in there. Are you sure you're getting 30 psi with the system idling? That's checking with MAX A/C, full cold, fastest fan speed setting? (window open)

The reason you're getting 60-70 psi static (engine off) is that the refrigerant is warmer (ambient temp).

If you want to change the orifice tube, take it to a shop that will evacuate the R-12 and change the orifice. Vacuum the system for 30 minutes and then put the R-12 back in.

black89ws6

On a system functioning normally, the compressor cycles out to keep the evaporator from freezing. In effect, it cycles out when cooling is not needed.

If it cycles out, and the system is running cold, then things are working correctly.

If it cycles out, and the system is not running cold, that would indicate a low charge, or other deficiency in the system.

On a hot enough day (85-ish, and above), the compressor will probably not cycle while the engine is idling, and the blower is on high. Remember, the compressor cycles when the compressor output sufficiently exceeds the system load (blower switch to low, engine rpm's increase, etc).

To charge by pressure, really requires a high side reading. Without that, you're better off charging by performance. Also, if there's a problem with the system, like a plugged orifice tube, high side pressure readings can help detect that.

tweakhat

my tpi car only came with single fan

mawinc

I have been retro-fitting cars 11 yrs. On most cars I only drain the compressor oil and replace with ester. I have not had one failure due retro-fitting. Start off with 80% of the r-12 charge and go from there. The pressure will be a little higher but it works just fine.