I just charged up my system and it took two 15oz. can's and the dial says it's full. Does that sound right?

Looking forward to cool comfort in Florida!!

 

What year is your car?

 

'79

 

Sorry I am not real good with conversion but I think in the shop manual you would be looking at about a 3 lb charge. that is what I used in mine it is a 79 as well... works fine.

 

Have done plenty of a/c work over the last 35 years. Usually an empty system takes at least three to three and a half 12 oz cans to do the trick. I usually put a a/c thermometer in one of the a/c ducts and watch it get into the shaded zone and use a set of a/c gauges when charging. I also vaccum the system first. Usually on the low side of the gauges you should be looking at 35-40 and on the high side a little over 200-250. If you are just adding some freon to the system and are using R-134A with just one of the small charging hoses I would just play it by ear or should I say feel. If it feels cold, just shut the can off. You could always add more down the road.

For the heck of it what do you mean the dial says its full. What dial are you talking about. Never seen a piece of a/c equipment that said that the system was full when charging the system.

 

You use 80 percent of the R-12 charge if that tells you anything...

 

The one on the dial on the hose that came with the retro-fit kit. Each area of pressure has a color code. If you are in the green area, you're supposedly good to go, or "full". That area is in that 35-45 range.

Maybe you can answer another question. I charged it up and everything seemed OK. Pressure on the low side was in the good area, and it cooled down nicely. I decided to go for a ride. About 2 minutes in to the ride, the compressor shut down and did not come back on. When I got back home, I put the guage back on the low side, and it was now showing about 100.

Any suggestions on what happened? The only thing I can think of is that that the high pressure switch shut it off, but what would cause the pressure to spike like that? It was fine for probably 5 minutes. (three minutes before I left and 3 minutes in to the ride).

I am getting REALLY frustrated with this.

Thank for the help!

 

I would guess you have a possible restriction in the line. Some of the GM vehicles had a ortifice tube in the line but I don't remember what year they started to use them. I am pretty sure your 79' has one. Usually the GM cars with the pancake style compressor have this. They are about the size of a cigarette and in one of the freon lines. They are like a filter catching any rust or dirt in the line and eventually become clogged. When this happens you stand a good chance of ruining your compressor if you keep using the a/c and or heater on your GM vehicle. Yes even during the winter when you turn your heater on the compressor will kick on when you turn the heater on unless you unplug the wiring harness going to the compressor. I have done that plenty of times during the winter time on my cars so if there was to be a freon leak I wouldn't burn the compressor out. If the line is clogged at the ortifice no freon or oils will pass in the line and you will kill your compressor. If you don't know where to look you are probably better off taking it to a professional before things get worse. There are times when someone puts to much freon in the car that can also cause some problems. You may want to try letting a little out to see what happens.

Question: Was your A/C system completely empty before you did the retrofit? If it was and you didn't let the original freon out you probably have a leak anyway. If it wasn't completely empty you may of mixed R-134A with R-12 and this may be a problem also. There are alot of questions to ask because I was not there to see what you did. If the system was empty from the get go any good professional would of vacuumed the system and did a leak down check before filling the system. What brand retrofit did you use? Did it come with a can of neutralizer for the difference in the R-12 oil verses the R-134A compressor oil? The good kits have this. If you decide to see if the orifice tube is clogged on your own you will need a special tool to take it out of the line. I found this out the hard way thinking a pair of needle noze pliers would do the trick but it only brakes the end off of the ortifice tube. Also once you break the line air will get in and destroy your receiver dryer and you should replace it because being opened it will suck all the moisture out of the air in minutes. There is alot to doing A/C when you have a problem. Hopefully your compressor is still good.

I have a 87' SS Monte Carlo I am restoring and the compressor went bad on this car. I am sure the orifice tube is dirty that caused this to ruin the compressor. Hopefully you are not in the same situation.

 

Your 79 has an orfice tube & it is situated right near the overflow container on the right fender...chances you will have to streighten out the aluminum pipe before you extract it...be careful it is old & will crumble you may hve to pick the tube out of the pipe make sure to remove it all...ps do not mix your refridgerents it makes for a messy situation. Sounds like you have a restriction.

 

CRUD. This is becoming not worth it, even here in Florida.

There was no R12 left in the system. The system had been opened, and before re-charging it with R134A, I had the system evacc'd out. He also left the guages on afterwards, to see if the system would hold the vaccum, and it did. According to the can, the R134A I used was compatible with R12 an R134A, so I assume that meant it had a neutralizer in it. But maybe I'm wrong.

As the compressor only ran for a matter of minutes before and after it shut off, I hope that there was no damage, as it was a new (rebuilt) one.

So, to get to the orifice tube, I'm going to have to have this Evacc'd again? At $30 a pop, this is getting ridiculous.

Receiver/dryer? Where's that? I didn't see one in the diagram. I got a condensor, compressor, orifice tube, accumulator, evaporator.

 

Recever dryer under & behind the overflow on the right hand side fender It's a hoot to get at I made my own wrenches to fit on the fittings to un do them..just cut the wrench. evac yes once the system is open you will need to vacuum it again I know it's a pain mine was similar...& remember if the compressor was a new one it should be ok but make sure you have the right amount of oil in the system...I think the compressor should have around 6OZ in it...did it come with oil? sounds like a plug orfice man..but hey it's air fun wow!

 

Is that similar or the same as an accumulator? I know at some point they changed the AC system. Do they have accumulator's AND receiver dryers, or is it one or the other?


According to the tag on the compressor, it came with oil in it.

I just don't have the money right now to go have it done professionaly.

 

Yes the accumulator is the same as the dryer basically just a different name. The early GM vehicles had separate dryers with a glass top so that you could see if there were bubbles telling you that you needed more freon in the system. The problem is when you open the system the accumulator or dryer will suck up moisture right away. If you reuses the old dryer with the system being opened your a/c won't be as cold as you would like it to be because of the bad part. That is why they come sealed from the factory and they need to be hooked up right away when changing them and then you need to vacuum the system which is the last thing you do before refilling with new freon. I would concentrate on pulling the oritifice tube out and then reconnecting the line with a new one installed before I did anything else. Remember to do this right a special tool for pulling it is required. When you have the money to purchase the accumulator and have the money to get it vacuumed then do the two together before refilling the system. If you feel you need more oil in the system that can be purchased in a pressurized can with about 2oz of oil.

When you own a Corvette the only way to save any money on repairs is to learn how to do alot of the work yourself. Just a word of advice. 35 years ago when I purchased my first Vette I didn't know very much. I was 19 yrs old and only driving at the time for 2 years but you learn as you go if you don't mind getting your hands dirty. I wish back then we had excess to the information that alot of the younger guys are getting on this forum. That would of been a big help. Going on this forum and asking questions and getting answers right away is the best thing that could happen for a new Vette owner.

One other thing I want to mention. You paid $30 to have your A/C vacuumed. If you have an air compressor at home Harbor Freight sells a vacuum pump for under $50 that works with your compressor. I own a Robinaire electric one that I purchased years ago during the 80's at actual cost being in the automotive parts business and it cost me $150 then. If you plan on doing other work it may pay for you to get one of those units instead of paying someone $30 everytime you need to have an A/C system vacuumed.

 

Did the cans have oil in them? If so how much oil did they have? The system should hold about 80% of the listed charge (38.4 oz) if every thing is working right. Does the comp clutch have 12 volts to it? If not do you have a DVOM to check to see what is holding it out; start with the high pressure switch than there should be either a low pressure switch our a thermostat some were to cycle the comp. My 77 has a thermostat on the inlet to the evaporator coil right after the orifice tub. Check for voltage there; if you do not have voltage there try the ground at the comp make sure it is good. If your system has a low pressure switch try there and see if you have voltage.

The high-pressure switch is there to protect the comp if the pressure did get that high (350 to 450 lbs) it should reset when the pressure drops. The low-pressure switch is there to cycle the comp if the pressure gets below 19 lbs or close to that. At this pressure the coil temp will drop below 32 *F and condensate will freeze on the coil blocking airflow. These switches fail regularly. GM has used this type switch on a lot of vehicles. I have replaced many. The thermostat was used on a few vehicles and it monitors the evaporator inlet temp if the inlet temp drops below freezing it will shut down the comp clutch off and when the temp comes back up it will cycle the clutch on.

If the comp was off when you checked and it was showing 100 lbs that would be normal.

There are a lot of things to take into consideration when charging a A/C system; ambient air temp; airflow; pressures in the system; cabin temp; without a set of service gauges it is very hard to trouble shot. Just a couple of things I can tell you about charging a vette. When the hood is open all the way about 30% of the condenser coil is blocked, so you need to lower the hood as low as possible. The correct way to charge the A/C is to idle the car around 1800 to 2000 RPM with a fan blowing into the condenser coil to simulate driving down the road.

Neal

 

I poured another can of Esther oil in the compressor before I mounted it. I also turned the compressor a few times to circulate it. The lube in the compressor is just for shipping and isn't enough for daily use. Then I vacuumed it down and refilled it.

JMHO.

 

Thanks guys. This is all good information.

The air was blowing nice and cold before the system shut down, so I hesitate to think it was the accumulator. The engine was on but the compressor had shut down when it showed 100 lbs. So if that's normal, maybe it isn't blockage.

Maybe this is electrical or a bad switch. I'll check it out.

Chevymans 77, you are quite right about doing things yourself. I actually just finished re-building the front and rear ends of this car, and I can't imagine how I could have afforded it if I had not done most of the work myself. The issue here is, I just have no clue about the A/C system, and that's why I come here. There is always somebody here who's been there and done that to help you through it.

Thanks guys.

 

check the electrical and let us know what you find, it could be the high/low pressure switch i thought they got replaced on a retro-fit to 134a

 

Is there a way of testing the high/low pressure switch without taking it out? At this point, if I don't have to open the system up again, I would like to avoid it.

I checked the easy part, and the fuse is good. So, it's not a blown fuse.

Any tips on testing the other electrical components. I do have a voltmeter.

 

Yes you can check the high and low pressure switches with your voltmeter. Turn the key to the on position and turn the A/C on. This should send 12 volts to the switches. Check for voltage at the high-pressure switch and at the low-pressure switch or the thermostat witch ever your system has. Check both sides of the switches to see if there is voltage, if you have voltage at one terminal and not the other than the switch is open and you have located the problem. Than next you have to determine if the switch is doing its job or if it is bad. If you find no voltage at the switches than you need to look at the controls inside the car and see if it is sending voltage to the switches. With 100 pounds of pressure in the system both switches should be closed an allowing voltage to pass through to the comp clutch. If your car has the thermostat than it is opened and closed by temp and not pressure. Keep posting and let us know what you find.

Neal

 

You are not going to open the system up by unscrewing the high and low presssure switch out of the accumalator. Take it out and just screw another one back in and see if that helps. I forgot to mention this to you before. These switches are cheap and I had one go bad on me before. They are a simple installation on most GM cars.

Fred