its 20 degrees...how 'bout and A.C. question?

[Chas]

there are 2 valves for my a.c. one on the compressor and one down the pass. fenderwall that is hard to reach....
my question is which one would i hook up a can of r-12 too?
they are both the same size fitting....most that ive seen , have 2 diffrent fitting and its impossible to do it wrong.
any help would be appreaciated.....:xmas

 

[smurfvet]

Find the one that is on a larger diameter line that goes from the firewall to the compressor directly. Better yet, look at the two tubes/hoses that are connected to the compressor as a reference. There are a total of three refrigerant hoses under your hood, so a brief explanation is needed.

One line, usually a smaller diameter, will go forward from the compressor connection to the condenser coil mounted in front of the radiator. A second smaller diameter line will run directly from the condenser to the firewall. This one is NOT conencted to the compressor. These lines are usually 1/2" or 5/8" diameter. The lines are both on the high pressure side of the system, so DON'T connect to those.

The third tube/hose should run directly back to the firewall, and is usually 3/4" outside diameter, or so. The line may be connected to a silver cylinder (receiver) that is mounted directly at the heater/evaporator housing. Look for a tap on this cylinder, too. It is usually under a plastic cap, if there. There is one on the newer GM units. That's the suction or low pressure line connection. Hook your valve hose to that one.

It is possible that the 1/4" fitting you described is on the suction connection at the compressor. If you check out the hose routing as described above, you can decide which fitting to use.

The older cars all had 1/4" SAE flare fittings on both lines, so it's easy to mix them up if you haven't done refirgeration work before. The newer R-134a systems and conversion kits use different size fittings so you can't mix them up. That's what you saw with the different sizes you referred to.

 

[mvftw]

When you add the R-12 should the can be upsidedown when adding?

 

[smurfvet]

The rule is: "if the can is upside down, you are adding liquid directly into a line that should be all vapor. Damage to the compressor can result".

With that said, if you "crack" or open the valve on the can "a little" and then turn it upside down to feed a small amount of refrigerant liquid into the suction line, you will "flash" or evaporate that liquid in the hose connection, even if the system is close to being correctly charged. The good thing is if you add liquid at a slow rate, the pressure in the can doesn't drop. You can tell this by the can not getting cold in your hand. The can does get cold if you feed refrigerant in with the valve "up". This is because you are flashing the liquid in the can to a vapor, which makes it cold.

If you are careful, you will be ok. If you rush it, you can seriously screw something up.

Another important issue is that the proper refrigerant charge amount is given in ounces of weight. Pressures work, to a point, but a charge by weight is the safest way to charge a car unit. That requires a very accurate scale or a charging cylinder.

 

[Chas]

Thanks for the wealth of information Al.

 

[smurfvet]

You're welcome!

One other comment- don't mix R-134a and R-12. They take totally different refrigerant oil and o-rings from what came in an R-12 system. Also, they are finding out the inner liner of the hoses is deteriorating when R-12 systems are switched over to R-134a.

If you are going to change over, you need to flush the system of the old mineral oil, add a "conditioner" to the system, add new PAG oil (synthetic), change o-rings and the low pressure switch if used, and evacuate the system.

 

[Chas]

it looks like everything is working except the cool....a friend gave the the r-12 and the hose...it will be the last so sooner or later i will convert it...after i find the right mechanic....this is fragile stuff and from what you have told me , i need a pro for the change over...im not sure this will work, but it was a freebie and i would like it to work. even though most of the time im crusin i have the tops off and in the back.thanks again for the help. i owe ya a cold one!

 

[cdhorn]

Hi:

I've converted about 5 systems successfully. They've been running now for two years with good results. The systems I converted were completely discharged, so there was not purging necessary. The conversion kits I've used are from Wal-mart and cost under $30.00. Since my systems were is such bad shape anyway, I wan't too worried about damaging any o-rings. If it didn't work, I wan't out that much and I didn;t have kool air before. The conversion kits come with oilcharged freon cans. This is the first unit that's added. The instructions tell you to add the oil charge and the first R-134 can with the can inverted. Subsequent cans are added with the cans upright. Since you are starting with a system that's empty, that's a pretty safe process.
One of my units, a 1988 Lincoln LSC hadn't required a recharge since it was done two years ago. My 89 Suburban went through several recharge cans and the 81 Corvette has used one refill can. I was very skeptical because of all the scary hype surrounding this process, but the process was very simple and has worked much better than expected. I'm suspicious that a lot of the scary type was from shops charging hundreds of dollars to convert. (Similar to the disc brake pad replacement cost)

I'm glad I did it. If I run into problems down the road, oh well, at least I bought some time before I have to replace a lot of parts. The real key is determining where the high and low pressure lines are. I bought a pressure guage just to be safe. The instructions are very clear as to the expected pressures and also how to determine the high and low pressure lines. The whole process takes about 1/2 hour, most of which is the recharging process.

Good luck

Clark

 

[Wills79Vette]

One quick question on the compressor if you dont mind. My compressor is not activating, and I cannot find any fuses for it, where should I look, its a 1979, thanks for your time.

 

[cdhorn]

The system has a low pressure cut-off switch which disables the compressor when the system is discharged to a certain level. Pull the 2 prong plug on the A.C. canister by the firewall, and jumper the two terminals together. This should cause the compressor to spin unless there is some kind of electrical problem. Once the system is charged to a certain level, the compressor will start cycling on it's own. It's best to buy a pressure gauge to determine a full charge, but if you don't have one, add freon until the compressor runs for a reasonable period of time without cycling or until the air coming out feels cold. The instructions in the conversion kit are quite good.

Good Luck

Clark

 

[jcompton]

I heard that the dryer chemicals can come apart and filter thru the system and stop the system up. It sounds like you (cdhorn) didn't do that but it seems to work anyway? I might try it at that level. Also does the r134 conversion have a sealing compound in the kit that gets installed also?

 

[cdhorn]

It comes with an oil charge can of freon that you put in first. It's supposed to lube the seals. If they leaked before, though, it will probably still leak a little. I had to add a can this summer in my corvette.