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Unloader's are used for capacity control and in the case of this semi hermetic compressor will unload the cylinders when the load on the cooling coil decreases. This topic is long but in short unloader's are added to a compressor to maintain suction pressure and saturation temperature.

You may as an example have a DX cooling coil and it is desired to maintain a 40 degree coil temperature. You will then need to figure out the suction saturation temperature in relation to refrigerant pressure. This equates to somewhere in the range of 68 PSI or 40 degree liquid saturation temperature at around 10 to 12 degrees superheat.

It is important to be with in the design range of the DX coil at all times and in the case of a system with a TXV it will hunt to maintain the desired superheat. Hunting of the TXV will depend on the load or conditions such as low evaporator air flow, or low ambient outside air temperatures, which will decrease head pressure.

When suction pressure is below the design it is desirable to begin unloading so that the suction pressure does not fall too low. When suction pressure is low the suction saturation temperature will also be low. Again you must consider the design which is normally 105 degree condensing temperature for R-22.

A system that works out of its design must be capable of handling this condition. Otherwise it is certain that problems such as oil migration or incorrect oil velocity through a system will occur and more than likely will result in a compressor failure.

You will have good results to load the compressor at somewhere in the close range of 68 PSI and begin to unload at around 62 PSI. I have seen many set to 66/59 but you are now out of the design range and saturation temperature will be as low as 33 degrees but above freezing.

There is much debate as to when to start unloading cylinders and in the case of a multi-stage unloading compressor it is important to figure out your design conditions first.

_____________________________________
Trouble shooting is not part of the repair......understand the symptoms and you will find a solution.

@phmtech
Follow the link in alcomechs post and read the second page.

Originally Posted by coolerik

Im Scarred

The compressor in this thread should be scared.

Hey all, Not meaning to hijack this thread ,but what is the purpose of the unloaders.? do they disable the cylinder? I have never run into these that i know of at the school corp. i am employed by.

Im Scarred

Just like hearing different outlooks on it. Yes there are people in my shop that can explain it to me why dose it matter? is this website not a tool to jet help as well?

So theres no one at your shop who you can ask how to do this or come to the site and show you?

thank you alcomech big big help..

Check this out

thank you

http://www.carlylecompressor.com/cor...TI1239,00.html

all i see is a smart unloader controller on carlyles website

Look on carlyles website, it has instructions on how to set up the unloaders.

Ahhhhhhh the old mechanical unloader. I don't know that by memory, I'm sure someone around here does though.

Attachment 336541

I'm guessing this is a copeland compressor? And is there a switch that looks like a low pressure switch wired to it?

And what application is this being used in?

how do you set your unloaders?

Valves like a solenoid valve? Pictures?

If I had to guess it would be unloaders.

we used a pump as well. now there was 2 valves on the top of the compressor by the low and high pressure ports. valves that can be adjusted with adjustable wrench is that some sort of equalizer?

Originally Posted by hvacman2213

sorry did not get back on the computer last night. yes it was a replacement its a 40ton unit with 3 OD fan motors that i think load or unload off the discharg line. The comp was sent to us with no oil in it i know how to get the oil in but how do you get it dialed in just right?

It's all good, we like giving people a hard time.

The compressor will say how much oil it holds, I'd start with half-ish of that and go from there. There are lots of ways to pull off putting oil into a system. I have always used an oil pump, I'd be interested to hear who does what.