Glass door freezer superheat

[Fridgy Dave]

Just wondering what the rule of thumb is with glass door freezer superheat. I have seen cases specified at 5k and flood back badly. I was told 10k but wanted to hear others opinions.
Thanks

[S.Palvi (jnr)]

Usually 5-7K yes, but if the compressor is situated lower than the blower coil remember a trap higher than the coil to prevent flooding. (asuming the coil is clean and optimal airflow is achieved)

[HVACRsaurus]

When you say flood back badly, is it just ice on suction of compressor, or is there a measured value of low/no superheat combined with other indicators such as cold discharge temperature and noises from compressor? As suggested in previous post, SH 5 - 7 DegK is normal, but often results in frost at the compressor - sometimes mistaken for floodback. Typical freezer systems normally have suction accumulator to provide some degree of liquid protection.

[Fridgy Dave]

Not sure whether this rack has an accumulator. Thanks for your input I will try and lower all superheat on all the freezers and see how the system runs.

[Magoo]

Hi Fridgy Dave.
do a forum search on superheat, there is a lot of discussion on subject to read.
magoo

[Fridgy Dave]

Thanks magoo I'll check that out

[S.Palvi (jnr)]

When you say flood back badly, is it just ice on suction of compressor, or is there a measured value of low/no superheat combined with other indicators such as cold discharge temperature and noises from compressor? As suggested in previous post, SH 5 - 7 DegK is normal, but often results in frost at the compressor - sometimes mistaken for floodback. Typical freezer systems normally have suction accumulator to provide some degree of liquid protection.

This is quite true, a colder discharge temp and a cold oil sump usually means liquid. A small SH of below 5 whould be the first indication of liquid overshooting, but also as Gary the VIP mentioned there is alot of factors that needs to be balanced out.