1981 C1500 factory air repair

[Kdsooner]

Hey members, I have a 1981 GMC Sierra Classic with factory air. It was my grandpa's truck and the compressor went out years ago. So in addition to purchasing a replacement compressor, what else do I need to consider? Sorry for the newbie questions, and if there's already a thread like this out there, sorry but I didn't find it when searching. I don't know much about converting to R134a refrigerant and what all goes into that. Is it a DIY job, or will I need to get a professional involved? Thanks for any info you can provide.

 

[Matt69olds]

Plan on replacing the orifice tube. It’s basically a small screen, it catches all the debris. Since the system is torn down, replace all the o-rings. Don’t leave the system open to the air, cover all the open ends of the lines with tape. Lastly, after your repairs are completed, evacuate the system with a vacuum pump. Close the valves, if all is well the system will hold a vacuum. Follow the instructions with the 134A conversion kit and recharge. Good luck

 

[Kdsooner]

Thanks. The lines are currently taped off. Can I evacuate the system myself, or will I need a professional for that part of the project?

 

[DoubleDingo]

Sounds easy enough, I need to do the same thing on mine. But first, find the second part of the AC bracket. DOH!

 

[animal]

Thanks. The lines are currently taped off. Can I evacuate the system myself, or will I need a professional for that part of the project?

If you have a vacuum pump you can do yourself. I don't have one but was able to borrow one from a friend. You might be able to rent one from a local auto parts store.

 

[yevgenievich]

Orifice tube, o rings, flush,and dryer. Replace hoses if old, add correct amount of oil and vacuum the system.

 

[Charlie]

 

[Matt69olds]

Thanks. The lines are currently taped off. Can I evacuate the system myself, or will I need a professional for that part of the project?

If you can rent the vacuum pump you can do the entire job yourself. Harbor freight use to carry a pump run by compressed air, the electric ones are more convenient. Either way, I’d rent or borrow a pump. The idea of vacuuming the system is to remove moisture. The lower the air pressure, the lower the boiling point of water. At 20 inches of vacuum, water boils at room temperature. The pump can then remove the moisture easily. Added bonus, if the system holds vacuum, you can be reasonably sure there are no leaks. Obviously, you can still have a leak that shows up only under pressure, but it’s a good diagnostic aid. Also, if I remember correctly, the charge of 134A is about 80% of what the old R12 system used. Don’t overcharge, the new stuff isn’t as forgiving. It was that big a deal to add a little extra R12 to keep the system going if you had a small leak. 134A doesn’t like that

 

[75gmck25]

I'll give you a general formula to use.
- Replace the compressor (R4?). I don't really like the rebuilt OEM R4s that much, but it might be okay. A better choice is a new Sanden and brackets from Vintage Air, and buy the block adapter to adapt it to your old hoses.
- New orifice. Generally, a Ford blue works better with R134a than your stock GM white orifice. They only cost about $3.
- Flush the condenser, evaporator, and the lines with A/C flush, and blow dry
- New Filter/Drier
- Convert the fill ports to R134a fittings (most kits include them)
- Reassemble with lightly lubricated new green (R134a) o-rings. Don't get carried away with tightening them down.
- Since you have completely cleaned the system, use PAG oil recommended by Sanden instead of the old oil used with R12. Sanden calls it SP-15, which is equivalent to PAG 100 or 150, but you will have to check.
- Draw 29" of vacuum for at least 30 minutes, then close it off and make sure it holds. Fix any leaks.
- Put the truck on high idle, and put a box fan in front to make sure you have lots of condenser air flow
- Recharge with about 75-10% of the R12 charge, but watch the gauges for optimum pressures. Pressures vary with ambient temps, but you never want the high pressure to go much above (ambient X 2)+ 50 degrees.

Bruce

 

[Stepside81]

Where do you buy R12 today? If you can find it, anyone selling it is sure to want an EPA Certificate? R12 was discontinued in 1994, yes/no?? I had a shop convert my system years ago to R134A because R12 as being phased out and future service with R12 would prove difficult, at best. But, I'm NOT a HVAC man.

 

[roundhouse]

Where do you buy R12 today? If you can find it, anyone selling it is sure to want an EPA Certificate? R12 was discontinued in 1994, yes/no?? I had a shop convert my system years ago to R134A because R12 as being phased out and future service with R12 would prove difficult, at best. But, I'm NOT a HVAC man.

There’s still quite a few cans floating around
And for sale on CL

I would use 12 on a system that’s fine but just need a extra can in it

If your system is already open I’d use 134 since you will Probabaly have to open it up again shortly after you charge it to fix the leaks you didn’t notice the first time
Or fix the new hose that the shop didn’t crimp properly etc

 

[RoryH19]

I converted my R10 to 134 four years ago.
At the time I also converted to a serpentine system from a 90 burb or blazer.
For the AC system I replaced the compressor, accumulator/dryer, evaporator, orifice tube, O-rings, hi/low side 134a fittings and rubber compressor hose. Needed a shorter one since the compressor changed sides during the serpentine swap.
I also added the PAG oil.

To recharge I went to a shop that has an A/C recharge system.
They evacuate the system, verify there aren't any leaks (hold vacuum) and charge with 134a to about 80% of the r12 amount.
For less than $100 it is worth having professionally recharged.

I live in DFW and with many 100+ days my A/C works great.