Automotive Air Conditioning Information Forum

Posting for my neighbor. About 10 years ago he changed from R12 to R134A without flushing the system. I am thinking that the oil has coagulated because the high side is reading 350psi when I get the low side to about 37psi.
Wondering if I can replace the condenser and dryer and flush the rest of the system including the compressor? or do I need to replace more parts.
Thanks in advance,
Steve

Hello, prairieschooner. A few questions to start. What is the make, model, and year of the vehicle? And did he leave the mineral oil in the system when he converted it to R-134a?

Sorry I should have posted 1985 Toyota Pickup. Yes he didn't know any better so all he did was to install a new compressor & dryer & add the oil that the kit from Napa included.
I have found the condenser and dryer but he is in his 80's and with limited income. If I can flush the other stuff it would be a great help to him but then don't want to waste his money by being incomplete.
Steve

Fan Clutch!

Is the compressor noisy? I wouldn't be surprised if it is because if he installed PAG oil on top of the old mineral oil remaining in the system, not only are they incompatible but the compressor also might be compromised...not to mention that there might be too much oil in the system. And since the high-side pressure is so high, the viscous fan clutch is probably shot, as Tim pointed out.

I would approach this by starting with a completely empty and internally clean system. Replacing the condenser and dryer (having R-134a compatible desiccant) is fine, but I would also consider replacing the ten-year-old compressor since its condition at this point seems questionable.

But before doing that, I would solvent-flush the evaporator (removed from the vehicle, if possible), plus all the lines and hoses without mufflers. Any hard or soft lines having integral mufflers and/or filters would have to be replaced.

I believe that this truck uses a conventional, not block-type, TXV. I would examine it closely for any defects, such as a crimped or cracked sensing-bulb line, which would require TXV replacement. Of course, o-rings should be replaced with the green HNBR type throughout. Denso was the OEM A/C parts provider, so I would choose new Denso parts if available.

If you're trying to save your neighbor some money, the original tube-and-fin condenser could be solvent-flushed as long as it's not externally corroded, damaged, or leaking.

The original specs I have call for 26 ounces net weight of R-12 and 7.5 fluid ounces of mineral oil. For additional tips on converting a system from R-12 to R-134a, check the topic "Minimum requirements for converting a system to R-134a" under "Automotive Air Conditioning Procedures, Tips and FAQ."

Lastly, please consider supporting this forum by calling Tim at ackits.com, the site's sponsor, for any parts you might need.

Thanks for your help and advice!

The Compressor didn't make any unusual noises and it appears that it was working with being able to withstand that extremely unusual high side pressure for the short period that I worked on it. But I am curious about the life expectancy now.
I will go by and let him know what we should do now with that advice.
Thanks for your help!

Oil will not mix, so there shouldn't be a coagulation issue. R134a is not carried well, so the concern should be more in the lines of a lubrication issue. If performance is an issue? Then I would be concerned with how the conversion was done component-wise more than blaming a mixture of oils. This vehicle is also known to have clutch fan failures. So if not locking up correctly, you certainly would have pressure issues.

With a high side of 350 PSI, the compressor definitely is still pumping. Incidentally, what was the approximate ambient temperature when you recorded the pressures?

If you and the truck's owner want to take a chance and re-use the existing compressor, be sure to oil-flush it a few times beforehand. That means flushing it on the bench using only the recommended PAG oil (usually PAG-46 for a Denso compressor). Be sure not to introduce any type of solvent into the compressor.

The process is to remove the compressor from the truck. Then drain out whatever oil is in the compressor, through the ports, by inverting it while rotating the main-shaft by hand using a socket wrench. Measure what comes out if you're curious about how much it contains, if any. Then, refill it with 5 ounces of fresh PAG oil and repeat the flushing procedure. Do this three or four times to ensure that you get out all the old oil. Then, refill the compressor one final time with 5 ounces of the recommended PAG oil and seal the ports until ready to reinstall the compressor. Distribute the rest of the oil as follows: 1 ounce each in the evaporator and condenser and 1/2-ounce in the receiver dryer.

Double End Capped (DEC) PAG oil is preferred over regular PAG because DEC PAG isn't hygroscopic--that is, it doesn't absorb moisture. If you can't find it in your locale, ACKITS.com probably has it in stock.

Thank You,
Temp was about 78 Degrees F.
Thinking we will flush the compressor since it was replaced with one from Napa and this truck gets very little use. Replace the condenser & Dryer and clean the rest of the system. All with your advice JohnHere
Steve

In addition to a reminder about replacing the fan clutch, I forgot to mention paying attention to the color of the old oil. Unless the system contains bright green UV dye for leak checking purposes, the oil in a normally operating system should be light to medium amber in color. Black looking oil that might also have foreign particles in it indicates a compressor that's self-destructing internally.