upright freezer

[sharonrod]

hi guys

could anyone help out with this? i went to check an upright freezer at a client. the compressor has already been changed by another tech. freezer uses r404a, compressor 14cc, capacity of freezer 600 litres. previous tech gave gas without weight, so i adjusted gas so that i have - 30 deg at saturation in evaporator, but temp on suction is 22 degrees, so super heat is very high.. probem is freezer is only going down to -17 and with such high super heat, am afraid that the compressor will not last long... what do you think the problem is?

[750 Valve]

So are saying this is a cap tube system? If so it sounds as if you may need a little more gas.

Also try posting in the appropriate section of the forum like commercial refrigeration - you will get more responses there

[sharonrod]

yes it is a cap system, but if i give it more gas, will then the gas work against me as it will also increase the temp at saturation in evap?

[taz24]

yes it is a cap system, but if i give it more gas, will then the gas work against me as it will also increase the temp at saturation in evap?

Saturation temp will only be accuratate if the air on and off the evap is about -20 / -25.

The best way to charge the system up is to jam the evap fan for awhile.
Slowly add the refrigerant untill the suction line frosts over. When the frost touches the comp stop charging and start the fan, run on test.

Just remember that 404a is a zeotropic and must be charged as a liquid.
Do not be tempted to add or remove as vapour.

Cheers taz.

[paul_h]

It's a capillary system, so charge by stated weight.
Subcooling and suction temp will be crap, but what can you do? They actually design them this way on purpose, to make evap pressure low and evap coils smaller than they should be.
ST will also always be high due to heat exchangers and/or oil coolers on these systems.
I've spent the last few years working on williams, skope and domestic fridges and freezers, they are all designed for critical charge and have high suction temps.
Reclaim evac and recharge to stated weight. If you want to play with it, the best way to get a non weighed, close as possible charge for a fan forced capliary system is to disable the evap fan, then charge until it's frosted back to the compressor. When the fan is reconnected, you've got as much charge as the system can handle without flooding back.

[750 Valve]

If you want to play with it, the best way to get a non weighed, close as possible charge for a fan forced capliary system is to disable the evap fan, then charge until it's frosted back to the compressor. When the fan is reconnected, you've got as much charge as the system can handle without flooding back.

+1 on this method but be sure to run it down to temp or return and check it when its pulled down.

[sharonrod]

thanks guys, you have been a real help