gs78vette

My 1978 has already been converted from R-12 to 134a but I bought the entire kit to "convert" it from 12 to 4a. Easier and I needed almost everything anyway, compressor went bad, etc.

My question is how much charge does it take. This is a package deal from Eckler's. Not sure if it is 2 lbs, 2¼ lbs, or what. Does anyone know for sure?
Thanks a lot.

72LS1Vette

You can buy a guage at auto parts stores that have 'low' 'good' and 'danger' (or something similar) ranges on them. You just have to plug the guage into the appropriate port and see what the reading is. You can check the readings while a can is charging the system so you will know when to stop. I use the guage every Summer because the daily drivers all seem to have AC leaks.



Rick B.

gs78vette

Thanks, just trying to plan ahead and wondered if someone knew roughly the limit on an empty.

Ganey

About 3. For R134a use about 85-90%. Orifice tube size should be changed for R-134.

08vycpe

I agree. I just did my A/C in my '79 due to a front seal leak in the compressor. I also recommend you replace the orifice tube before you do any charging. You can get a direct replacement orifice tube for about $.88 to 6.00 depending on where you buy it. I would recommend one of the new variable orifice tubes that cost around $20-30. It will help the vent temps a lot. Be careful about removing the old orifice tube as it is very old and the plastic is brittle and can break off in the pipe easily. You can rent an orifice tube removal/installation tool free from Autozone and I highly recommend it.

Also, don't forget you have to draw down a vacuum for 1/2 hr to an hour before you charge the system.

The old R12 mineral oil is not compatible with the R134a refrigerant so you have to be sure to get it all out of the system with a pressure flush. You should also replace the accumulator/dryer as it will be full of old oil and you should never flush the system through the accumulator/dryer or the compressor. Drain the old oil out of the compressor and put some Ester oil directly into the compressor before reinstalling it. The R4 compressor only takes about 5 1/2 oz of oil in the system where the A6 takes about 11 oz. Don't overfill the system.

You can use PAG oil or even better yet use Ester oil as the Ester oil is compatible with both R12 mineral oil and R134a refrigerant.

As mentioned, charge until you get the correct pressure on the guage but never more than 3 cans. Get the guage that screws on with the can so you can read the pressure as you are adding the refrigerant. Add the first can upside down and the other 2 right side up. You need to add the first can without the engine running to get enough into the system to turn on the compressor. Otherwise the pressure switch will prevent the compressor from running. A fan running on high in front of the car pushing cool air into the condensor will help draw in the refrigerant faster as well.

Just passing on some recently accumulated knowledge as I just did my A/C system.

gs78vette

Thanks a lot folks, great info! I do have a new orifice tube, the old one was not in correctly either. I now have a new (remanufactured) compressor, orifice tube, dryer, oil, seals, fittings, & adapters.
http://www.ecklers.com/product.asp?p...2&dept_id=1190

That's a lot of very specific info, O8vycpe, I do appreciate it and to everyone that responded.
I should be able to get through this with some confidence. Plus that, it seems that all of you generally agree on the parts & procedure.
Anxious to get it done now!

wtbrs123

courious how do you draw down a vacuum? what equipment do you use? I have a 79 L82 my a/c does not work low on freon. I will bring it to an a/c shop to get it repaired.
I want to know a little about this process so I can hold my finger on the cost.
I spoke to two shops they are already talking about haveing to change this and that have not even seen the car. They maybe right I just what to feel good about it.
I was told that the 79 system is not a barn burner should i just change the system out for newer better? your opinion please.

08vycpe

wtbrs123: If you do it yourself you will need a vacuum pump capable of pulling around 27-28" hg. I bought this one from these guys. Just connect it to the low side fitting and turn it on. I have a guage set as well and you should close the fitting after you draw down the vacuum and let it sit for 1/2 hour to be sure it holds the vacuum. If it doesn't you have to find the leak and fix it. Some pumps come with the guages as well in a kit.

http://www.usatoolwarehouse.com/usat.../FJC-6909.html

If you take it to a shop they will purge the system, filter the refrigerant and use it again. By law only a licensed A/C person can purge refrigerant from a system. If the system is already empty or low you can charge it back up yourself or they will charge you for a full charge.

If you have a leak the shop will have to find the leak, repair it, purge, evacuate and charge the system at the least. I don't see how you could get out of there for less than $350.00.

My '79 A/C system now works well with the new compressor, accumulator, orifice tube and R134a refrigerant. Your vent temps will be higher if you use a direct replacement orifice tube and lower if you use the variable one so I would suggest you go with the new variable one.

gs78vette

@O8vycpe or whoever knows A/C (orifice tube)

As stated/shown previously, I purchased the A/C kit from Ecklers which included a direct replacement orifice tube (I assume). That variable orifice tube sounds like it would be worth the higher price overall.

I had not even heard of it until it came up in this thread. Can I get that at most any auto parts store or is that something that has to be ordered elsewhere?
Also; is there just one kind or do I need to ask for a certain one to fit this A/C kit and does it fit like the direct replacement? I really appreciate the help, A/C is not my area.

Ganey

Some factory systems were converted from R-12 to R-134a by only 1 mech. change- reducing the orifice tube!
Some A/C shops are changing the GM orifice tube to a smaller Ford tube which has 2 O-Rings to seal better.

Probably changing the GM white orifice tube .072 to the Ford red .062 would be best orifice tube.

gs78vette

Thanks Ganey

I think that is how it turned out. I went to the auto parts store and told them what I had, what I was doing and they said said the one they sold me was used about 98% of the time. It was the red color.
I said to show me others since some other configurations were available and they had a green one with a "cross stop" at the end. That was all they had.

The instructions did show that the red one replaced a number of the other ones (different colors). I therefore tend to agree with you Ganey, it appears to be the right one. I'll find out tomorrow. Thanks for the reply.

Kfmorgan

I am also someone who did not know about the orifice tube. I just recharged mine with the 134, but would like to get it a little cooler. Where is this tube located, and how much of a problem is it to replace?

Ganey

The orifice tube is on the pass. side in the line from condenser in front of the evaporator case & below the line connection. Disconnect this line connection & pull orifice tube. Of course the freon has to taken out first. GM has a .062 orifice tube.

08vycpe

Changing orifice tubes is as we have all mentioned a good idea when converting to R134a. You can get a variable orifice tube from your local A/C shop or here is the genuine Delco part number for your 1978 Corvette for $23.00.

http://parts-catalog.acdelco.com/b2c...=SEARCH_REVIEW

Kfmorgan

Thanks for the info! I wish that I had known that before I recharged the system.