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Forum Index => Refrigerator & Freezer Repair => Topic started by: Qamar on March 31, 2012, 12:37:10 AM

Title: sub-zero
Post by: Qamar on March 31, 2012, 12:37:10 AM
I am working on s/z mdl 680/s the problem is fridge side display shows 42* f and my thermometer shows 49*f  sp is15psi and lp is 95psi are these pressure ok for R134A this is the first time working on sub-zero wondering what should be the normal pressure for both  in 85*f ambiant temp.
 
Title: Re: sub-zero
Post by: JWWebster on March 31, 2012, 08:55:37 AM
15 PSI seems high to me but I have heard others mention 15 PSI before. I like mine to be around 5 PSI. You know you have too much when the low side frosts over at the compressor. Are you seeing that? You can also check the amp draw. If it is over amping that is also a sign of an over charged condition.
Title: Re: sub-zero
Post by: jumptrout51 on March 31, 2012, 05:39:38 PM
15 is too high. 5 to 1 is best.
Title: Re: sub-zero
Post by: tgoods on March 31, 2012, 08:52:27 PM
I hate to say it but you're both wrong.  The 680 has a cut-out pressure of 16psi and cut-in 36psi on the low side. Should be 90 to 100psi on the high side. If the refrigerator is cycling, I'd say you have a bad cold control.  If it's running constantly but not reaching temperature, you probably have a leaking evaporator. Subzeros have a 12 year warranty on the sealed system parts.
Title: Re: sub-zero
Post by: ApplianceGuru on March 31, 2012, 10:24:44 PM
Some Sub Zeros require a higher low side pressure.

At sea level, most small appliance refrigerators charge at 4 or 5 psig.  If you are at mile high level (Denver) then you charge to around 0 psig.  Your gauge measures relative to outside air pressure.  At higher elevations, the pressure is less, therefore your gauge reads less psi.

The best method of charging is superheat.  It's the only way to ensure you are not getting any liquid refrigerant back to the compressor.

Does anyone know the acceptable superheat charge for small appliances??
Title: Re: sub-zero
Post by: jumptrout51 on April 01, 2012, 07:42:52 AM
I hate to say it but you're both wrong.  The 680 has a cut-out pressure of 16psi and cut-in 36psi on the low side. Should be 90 to 100psi on the high side. If the refrigerator is cycling, I'd say you have a bad cold control.  If it's running constantly but not reaching temperature, you probably have a leaking evaporator. Subzeros have a 12 year warranty on the sealed system parts.
Do you have a Tech Sheet or 680 specific manual you would share?
Title: Re: sub-zero
Post by: RegUS_PatOff on April 01, 2012, 08:32:27 AM
680 has a cut-out pressure of 16psi and cut-in 36psi on the low side. Should be 90 to 100psi on the high side.

that is correct ... (for the Fridge side)
Title: Re: sub-zero
Post by: Qamar on April 03, 2012, 10:13:05 AM
Thanks for all the help I loved all the info from Jwwebster, Tgood and appliance guru. I will have slight disagreement w/tg if low side leaks than sp will be lower than 1 psi, but i will go w/ temp control.
 thanks for all the help
Qamar
Title: Re: sub-zero
Post by: JWWebster on April 03, 2012, 11:19:05 AM
I could see how it might need higher pressure on these wonders. They have 2 evaporation zones so naturally the pressure might need to be higher. Highly over-engineered garbage is what I call it.