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Originally Posted by Gary
Apparently the system worked adequately for many years, and the evaporator has not been changed, nor the piping. ^
Correct, nothing changed. We did such a rtrofits already many times, never had these problems.
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The pistons have broken twice, for reasons that are less than satisfying, once with R22 and once with R404A. I would be curious to know if any repairs were done prior to the first compressor problem, and what those repairs were.
Even better, just opened this afternoon the new compressor and this is what I found:
* Oil quantity: +/- 5,5 l., so this is OK.
* Oil was grey, due to very small aluminium particles.
* 1 of the 4 pistons broken in 20 pieces,
* 2nd has almost 2 mm spacing on the crankshaft and should have broken any time if we hadn't opened it.
* Piston 3 and 4 seems OK.
* Valve plates OK.
I removed the melted aluminium on the crankshaft with HCl and there are almost no scratches on the shaft.
I was surprised that I could remove this so easily.
I also see some small copper color traces (actually more spots). Copperplating?
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There are a lot of R404A systems out there that are not having oil return problems, as far as I know.
That's also why it's bothering me.
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I am torn between viewing this as a floodback problem or an oil return problem. Possibly it is both.
Due to the fact that oil quantity is OK, it's more a floodback problem.
Saw also this morning when we removed the compressor that client had installed an additional time delayed contact between the SV so that they can shut down the compressor for some minutes when they're in the freezer to work.
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We are missing something here.
Sure, I'm also guessing what the cause can be for all this problems and that's also why I'm asking you, the pro's, for advice.
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What temperature is the freezer? Evaporator air in and air out temps might tell us something.
Temperature in the freezer is set at -20°C. Will measure air in/out probably beginning next week.
The last time, we measured subcooling and superheat, LP and HP, AMPS on the 3 lines, oil pressure because we needed to fill in this figures on the warranty papers.
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If the solenoid opens, and there is a significant delay in starting the compressor, the entire refrigerant charge can migrate to the coldest point, i.e. the evaporator. When the compressor starts, this can come flooding back. The larger the charge, the higher the danger.
SV opens when thermostat asks for cooling, and compressor starts then in less then 5 seconds.
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Also, if the defrost is terminated by time duration rather than temperature, the fans will start immediately.
Defrost is stopped on temperature (+8°C) and additionally with a safety time delay (45 minutes)
A normal defrosting takes +/- 25 to 30 minutes.
But,... the fans can not start as long as the evaporator coil senses temperatures higher than -5°C.