Troubleshooting AC leak before charging with R134a

[XfireZ51]

Thx 1991. Very interesting and informative. How would u say the proper valve compares w the omes you bought?

[1991 Corvette ZR-1]

Originally Posted by XfireZ51

Thx 1991. Very interesting and informative. How would u say the proper valve compares w the omes you bought?

The tiny valves in the assortment link I posted are a perfect fit for replacing the cores the switches connect to. The larger cores were not a correct size height wise. Once threaded in, the stem sticks out above the opening. Too tall. Even with the R134a adapter threaded on, the gauge connection would not fully seal due to the stem.

And it does flow properly. I held vacuum on the lines for several hours and then released it through the high side, so I know I have proper connection now. One of these days I might finally put refrigerant in.

[1991 Corvette ZR-1]

World?s slowest ZR-1 mechanic here. I found some valuable info from 2013, courtesy of Scottfab posting. These steps below differ slightly from the 1991 FSM recharge procedure on 1B1-23. See Below:

Charge the A/C System
1. With both Manifold Valves closed, hook up a can of R12 to the yellow middle hose (see Note #1 below).
2. Turn the can valve fully counterclockwise to open the valve.
3. With the can upright, crack the fitting on the yellow hose where it attaches to the gauge manifold to purge the air out of the hose, then re-tighten it.
4. You can now invert the can and crack the blue Low Side valve and charge until the pressure equalizes between the can and system (no more flow is felt or heard). Never open the Red High Side valve during the Freon Charging process.
5. Now start your car and set the climate control for Max cooling with blower on high. Ensure that the compressor clutch is engaged at this point (see Note #2 below). You can now charge the remainder of the first can with can in an upright position. Always charge with can upright when compressor is running.
6. Once the first can is in, (you'll know it's all in when you can shake the can and not feel any liquid sloshing in it) you can shut the low side valve and swap to the second can.
7. Remember to purge the yellow line again prior to charging.
8. Continue this until you have added the correct amount of Freon, per the FSM. Once the system is fully charged, shut off the compressor and allow High Side and Low Side pressures to equalize before disconnecting the gauge manifold from the system.
9. Once the manifold is disconnected, cap the high and low side fittings, reconnect the pressure cycling switch and you're done.


The FSM approach in a nutshell:

1. Start engine first before any refrigerant is added. Set AC mode control button to ?off?

2. With refrigerant can inverted, open valve and allow 16 oz through low side connection

3. After 16 oz added, engage compressor with controls and set blower speed to max. (May need to jumper low pressure cycle switch to turn on compressor during recharge process).

It sounds like the engine can either be on or off during the initial inverted can fill. Then when 16 oz is added, engage compressor on already running car, or start car and turn on compressor immediately. Regardless, can should never be inverted while the compressor is running, is what I have read.

There are 12 ounces in one can of R134A that I have. According to the FSM instructions, I will completely empty one can alone just on inverting it (upside down) and introducing to the system with the vehicle off. Then I need to have four extra ounces of inverted added THEN I can start the engine.

So 16 oz in a pound means I need one pound of R134A introduced to the vacuum tight system BEFORE starting. Then with the engine on, I use an upright can and add another full can of R134A.

That would put me at the following procedure:

1st can - upside down, open valve on low side, completely empty into system

2nd can - upside down, open valve on low side, extract 4 oz ONLY, measure with electronic scale to verify, set this can aside

Start car, engage AC compressor, blower to max setting

3rd can - Right side up, with car running, open valve on low side and introduce entire can for the full 12 oz.

This will give me a total of 28 oz of R134A in the system, which works out to 1.75 lbs.


Per an old post by -=Jeff=-

?R12 at 2.25 will be around 1.8lbs (at the high end) of R-134a

Typically R-134a is about 75-80% of the R12 fill.

reason the later cars are at 2lbs vs 2.25 is the added capacity of the parallel flow condenser vs the tube and fin condenser?

So that last .5 of an ounce I will have to gently add in I suppose. Sorry for the novel but just thinking out loud on my game plan before I start pumping refrigerant.

[-=Jeff=-]

Originally Posted by 1991 Corvette ZR-1

That would put me at the following procedure:

1st can - upside down, open valve on low side, completely empty into system

2nd can - upside down, open valve on low side, extract 4 oz ONLY, measure with electronic scale to verify, set this can aside

Start car, engage AC compressor, blower to max setting

3rd can - Right side up, with car running, open valve on low side and introduce entire can for the full 12 oz.

This will give me a total of 28 oz of R134A in the system, which works out to 1.75 lbs.

You might not get 2 cans in without the car running, depending on ambient temp as well.. the vacuum up previously pulled and still have on your system with pull only so much in, you may need to finish can 1 and can 2 with the car running and the compressor running. I also found placing the can in hot water (higher than ambient) will help 'push' the refrigerant out of the can

[1991 Corvette ZR-1]

Originally Posted by -=Jeff=-

You might not get 2 cans in without the car running, depending on ambient temp as well.. the vacuum up previously pulled and still have on your system with pull only so much in, you may need to finish can 1 and can 2 with the car running and the compressor running. I also found placing the can in hot water (higher than ambient) will help 'push' the refrigerant out of the can

I just wanted to do a quick follow up that I charged the system. I may not have the optimal amount of R134A in the system because the vent thermometer was only reading 50 degrees on level 10 blower setting. Although that may be the best I can get? Wondering how other DIYers made out on their cabin temps. I had the setting on AUTO and blower on 10. Also have done Marc?s blower wire upgrade as well. Passenger side window was all the way up with the driver side slightly cracked.

[ghlkal]

1991, thanks for all the information

Originally Posted by -=Jeff=-

I also found placing the can in hot water (higher than ambient) will help 'push' the refrigerant out of the can

That's a good idea, Jeff. I'm trying that the next time I need to put some in.

Originally Posted by 1991 Corvette ZR-1

the vent thermometer was only reading 50 degrees on level 10 blower setting. Although that may be the best I can get? Wondering how other DIYers made out on their cabin temps.

That is better than I get. IIRC, my system is closer to 60* than to 50*.

[1991 Corvette ZR-1]

Originally Posted by ghlkal

1991, thanks for all the information



That's a good idea, Jeff. I'm trying that the next time I need to put some in.



That is better than I get. IIRC, my system is closer to 60* than to 50*.

Thank you, sir! Hopefully it can help someone else out along the way. Maybe the increased blower speed thanks to the added 12 gauge wire helps? If I remember correctly, the added 12 gauge wire with a fuse tied into the red blower module wire helps increase the air output by 4%. Maybe that extra 4% helped inch me closer to 50 degrees? I am also unfairly comparing this to a video posted on YouTube recharging AC by ChrisFix where his thermometer reads 43 degrees at the vent. That system on that vehicle was designed to work with R134A from the start whereas most of us are trying to make the old R12 systems work at that level in a conversion.

Though I have to wonder if the replacement condenser had different sized tubes for R134A or if they keep the reproduction parts the same tube diameter. Well to breathe some life into this old system, off the top of my head.

New condenser $100
Accumulator $25
O rings $5
New compressor lines $150
Compressor rebuild kit $20
Compressor oil with dye $20
Vacuum and gauges kit $150

So $470 worth of stuff and I would say round it up to $500 for little things like R134A adapters and the Dorman plug and other little bits. Not bad.

[1991 Corvette ZR-1]

40 degrees! Not using my thinking cap, the vehicle turning higher rpms cools better than at idle. On AUTO at speed, it got to 43 degrees with max blower and I was pleasantly surprised. For max cooling, per FSM, I selected circulate and with blower on 10 was I surprised to see the thermometer showing 40. Any worries about not having enough R134A in the system have been eased. At idle, the thermometer does creep up to 60 degrees, and the cooling falls off noticeably. Probably didn?t help that I had the clear top on. Very happy with the results so far.

Next on the list will be a replacement AC clutch as the final touch one day. The world?s slowest ZR-1 mechanic finally finished this project.

[-=Jeff=-]

when you guys are posting outlet temps of your AC, what is the Ambient Temperature? I found, the blower on mine gets good voltage, air velocity out the vents equlas that of my 2016 Charger, but the volume it not there. It will get the car cool on a hot day and the coolant temp hangs around 200-210 depending on type of driving ( traffic or moving)

[HAWAIIZR-1]

Thanks for sharing all your trial and tribulations. I found my AC was not cold and the compressor not engaging due to low pressure, but no codes. I charged with 1 can and bingo it works. But after I took off the line the low pressure Schrader valve is leaking. I fiddled farted with it trying to stop the leak, but I don?t have as new valve or the tool to change it. So I?m waiting on the valve core tool and the tool to replace the valve if needed without freon discharge. When it comes to AC I?m totally clueless, but I?ll learn with posts like these and YouTube.


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