R12a Evacuation/Recharge

[caseyrstewart]

On 6/24/2019 at 8:19 PM, Minuit said:

I doubt that you can buy a new compresor with mineral oil in it these days. I'm guessing they are always expecting an R-134a conversion regardless of what the original system was.

 

Drain out as much of the PAG oil as possible and replace it with mineral oil. Turning the compressor as you drain it out will help get more out. You won't get it all, but you'll get most of it.

 

Before you add oil, tell me how much PAG oil came out of the replacement compressor. If it's a full system charge worth (6-8oz), add the 3.5 oz we discussed.

 

Was able to drain out 5.25 fluid ounces. Do I need to put O rings on the valve fittings that transfer from the old compressor to the new one?

 

 

[caseyrstewart]

Ok. Here are my results after installing the new A/C compressor and recharging with Red Tek 12a:

 

-Drained PAG oil from compressor and added 3.5 ounces of mineral oil

-Kept original dryer installed (only about two years old)

-Reinstalled fittings with all new O rings

-Pulled vacuum at held at -30 mg for approximately an hour

-Added (3) 6 oz cans or refrigerant

-Manifold gauges read 19 PSI on the low side and 200 PSI on the high side

-Outside temperate was 83 degrees Fahrenheit

-New compressor engages and runs

 

So obviously something is still not right. It blows cool but not cold in the cabin. Anyone have any thoughts?

 

 

[Minuit]

Got a probe-type thermometer? Stick it in the center vent and tell me what it says both sitting still and driving. I know for a fact my R-134a system always produces air in the mid to low 40s at highway speed. Sometimes it feels like it's about to freeze my hands off, sometimes it doesn't. Put some numbers to the situation and we can know better for sure.

 

For R-134a, that pressure is approximately correct. I would've thought it should be a little lower on 12a, but who knows. Try spraying some cool water on the condenser and see what happens to the high side pressure. If you see a big pressure drop, there's an airflow/condenser performance problem.

[caseyrstewart]

6 hours ago, Minuit said:

Got a probe-type thermometer? Stick it in the center vent and tell me what it says both sitting still and driving. I know for a fact my R-134a system always produces air in the mid to low 40s at highway speed. Sometimes it feels like it's about to freeze my hands off, sometimes it doesn't. Put some numbers to the situation and we can know better for sure.

 

For R-134a, that pressure is approximately correct. I would've thought it should be a little lower on 12a, but who knows. Try spraying some cool water on the condenser and see what happens to the high side pressure. If you see a big pressure drop, there's an airflow/condenser performance problem.

 

Ok, so I didn't spray the water on my condenser. Instead I figured I'd go for a drive with the thermometer and wow, I must say, it's significantly better than last night! I measured 53 degrees at the lowest point while I was driving about 45 MPH (outdoor temp was 83 degrees). Makes sense considering it was just sitting idle in my driveway and there was no airflow through the condenser. 

 

Still not freezing cold, but MUCH better and I could live with it if you say that's as good as it's going to get. Is that about the ballpark temperature I should expect or do you think adding more refrigerant would help? My apology if these seem like dumb questions. I do live sound for a living. Ask me how to put on a concert for a stadium full of people and I'll tell you anything you need to know!

 

[Minuit]

It's totally normal for AC to work better at speed than at idle. A factory style condenser will make this even more noticeable as it's less efficient than a parallel flow one. For a supposed "R-12 substitute" as a refrigerant 53 isn't very impressive, but it's better than nothing. This is the phase where you can easily make things worse trying to make it better. For what it's worth, that's about what my original system did with all of the old parts and a subpar R134a retrofit. I would've been fine with it if the system was reliable, but it wasn't. That led me down the path that got me here. At the end of the day, you've got to ask yourself if the AC works well enough to satisfy you.

 

If the spray test causes a large pressure drop, investigate your fans. The refrigerant has to turn from a gas to liquid in the condenser, and if it doesn't, the system won't cool worth a damn. The airflow over the condenser is what pulls the heat out of the refrigerant after it gets pumped up (getting hot in the process)

 

Leave the charge alone. The number I gave you is based on Red Tek's numbers.

 

[caseyrstewart]

On 6/27/2019 at 11:21 AM, Minuit said:

It's totally normal for AC to work better at speed than at idle. A factory style condenser will make this even more noticeable as it's less efficient than a parallel flow one. For a supposed "R-12 substitute" as a refrigerant 53 isn't very impressive, but it's better than nothing. This is the phase where you can easily make things worse trying to make it better. For what it's worth, that's about what my original system did with all of the old parts and a subpar R134a retrofit. I would've been fine with it if the system was reliable, but it wasn't. That led me down the path that got me here. At the end of the day, you've got to ask yourself if the AC works well enough to satisfy you.

 

If the spray test causes a large pressure drop, investigate your fans. The refrigerant has to turn from a gas to liquid in the condenser, and if it doesn't, the system won't cool worth a damn. The airflow over the condenser is what pulls the heat out of the refrigerant after it gets pumped up (getting hot in the process)

 

Leave the charge alone. The number I gave you is based on Red Tek's numbers.

 

 

I think I'm just going to leave it alone. Like I said, I don't drive the truck very often. Plus the cabin is so small that it doesn't take that long to cool off. I just hope I got the leak by changing out the compressor. Like you said, as long as I can rely on it staying 53 degrees consistently, I'd call this repair a success. If in two weeks it's back to blowing hot, I may have to dig in a little deeper. 

 

Thank you so much for all your help and knowledge! It's greatly appreciated!!