Restaurant cooler repair

Last couple days, I've had the chance to work on a reach in cooler, at a restaurant. Under a counter. The old guy who runs the place says it needs freon every six months. The aluminum evaporator gets wet, and probably has a lot of pinhole leaks. I checked all the fittings, and find no leaks at fittings or braze joints. Metering device is TXV, and the system has a receiver.
The system is probably 30 plus years old. The evaporator is above the compressor. About 8 inches higher, and maybe six feet to the side.
Since the evaportator his higher, perhaps oil return isn't an issue. Since it runs off a TXV, maybe it will adjust to the lower heat capacity of 134a. Has anyone else tried such a conversion? I'd much rather be feeding it 134a, compared to some other gas or blend.
--
Christopher A. Young
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Stormin Mormon wrote:

I put UV dye in an old walk in cooler system. When I shined my UV spotlight on the receiver, the tiny pinhole leaks lit up like a starry night sky. Replaced the receiver and no more refrigerant loss. I did change an old R-12 walk in cooler over to R-134a until I could tear it down and pressure check every section to find a leak. To change it over required removing as much mineral oil as possible and adding POE oil and refrigerant stop leak. The system ran fine for a few years until the owner decided to spend the money on a proper tear down and leak hunt. The R-12 expansion valve was happy with R-134a and required no tinkering. There was some fiddling with the pressure switch but it was a pump down unit with a solenoid valve controlled by the cooler thermostat. I've had very good luck with this product:
http://tinyurl.com/otxsfg
TDD
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I put UV dye in an old walk in cooler system. When I shined my UV spotlight on the receiver, the tiny pinhole leaks lit up like a starry night sky. Replaced the receiver and no more refrigerant loss.
CY: Also a very possible leak. I don't have a UV leak stuff system, but maybe this is a good reason to consider one. Used to have a bottle of red dye, for much the same reason.
I did change an old R-12 walk in cooler over to R-134a until I could tear it down and pressure check every section to find a leak. To change it over required removing as much mineral oil as possible and adding POE oil and refrigerant stop leak. The system ran fine for a few years until the owner decided to spend the money on a proper tear down and leak hunt.
CY: In this case, that would mean unbrazing the compressor, and unbraze the process stub. Tip out the mineral oil, and pour in same volume of POE. I sense that's a bit of work. Compressor change out typically takes me three hours. I wonder if there would be enough oil return, with gravity, to keep the oil out of the evaporator.
The R-12 expansion valve was happy with R-134a and required no tinkering. There was some fiddling with the pressure switch but it was a pump down unit with a solenoid valve controlled by the cooler thermostat.
CY: I can imagine it would take a different pressure setting. Probably down a couple pounds. But, that's something I can set by the actual performance of the unit. This unit controls temp with the pressure switch. No liquid line solenoid.
I've had very good luck with this product:
http://tinyurl.com/otxsfg
CY: Thanks. I've seen people mention that leak stop stuff. Might work. I should try a can of it. Suggest it to the restaurant guy.
TDD
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Stormin Mormon wrote:

One thing I should mention is that when I change over a small system, (compressor burnout), I have a couple of Q-size nitrogen cylinders and injectors that I use to blow system flush through the tubing and evaporator/condenser. If you get the right compressor, you may not have a problem with the cap tube when it comes to capacity if you go back with R-134a. I personally like to use R-416a which will sub for both R-12 and R-134a. The R-416a runs a lower head pressure than R-12 and will work with either oil. It is recommended to use alkylbenzene or POE oil if you have an oil return problem but I've never had problem using 3GS mineral oil in a system with R-416a.
TDD
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One thing I should mention is that when I change over a small system, (compressor burnout), I have a couple of Q-size nitrogen cylinders and injectors that I use to blow system flush through the tubing and evaporator/condenser.
CY: Yes, that sounds wise. Get the acids out. Fortunately, we're not at burnout, on this system. Yet.
If you get the right compressor, you may not have a problem with the cap tube when it comes to capacity if you go back with R-134a.
CY: The system I'm servicing has a receiver. So, in theory it should feed liquid The metering device is TXV, so it's got some kentucky windage, as to delivering refrigerant.
I personally like to use R-416a which will sub for both R-12 and R-134a. The R-416a runs a lower head pressure than R-12 and will work with either oil.
CY: When it came out, I got some 409a. Supposed to drop right in, to sub for 12. Problem is, you have to deliver liquid. Either pump it into the liquid side, or flash it to vapor before it gets to the compressor. Which, 409a, is more expensive than 416a, I find out later. Didn't know you could sub 416a for both of those. 134a is a bit cheaper than 416, I think. I'd love to load the beast up with a couple pounds of R-22, I still have a bunch of that. But, the pressures are a bit too high.
It is recommended to use alkylbenzene or POE oil if you have an oil return problem but I've never had problem using 3GS mineral oil in a system with R-416a.
CY: Good to know. Thanks. Ideally I'd like something like 134a so I can use vapor to charge the system. No risk of slugging the compressor.
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Stormin Mormon wrote:

I have a couple of charging adapters that allow liquid charging. One is a simple tiny orifice that you can screw on anywhere on the low side line or refrigerant cylinder. The other is about the size of a small fist with expansion room.
http://tinyurl.com/otvo8s
http://tinyurl.com/qzm4es
TDD
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well.....since you don't want to fix it right, you could try this: 1. insult the customer. try a smart-ass answer to any questions he might have. 2. Add any refrigerant that you want to, because on a system that old, anything other than R-12 is probably going to put too much stress on all parts of the system, leading to failure soon. 3. Insist on cash payment, after all you wouldn't want to have to pay taxes on that 4. Wish him a nice day, and give him some literature about the LDS church. 5. In about six months, wonder why he hasn't called you back out.
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Would you suggest about 8 pounds of R-22 would be about right?
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Christopher A. Young
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