Most small hermetically sealed compressors are protected from heat damage by a thermo switch that stops compressor when it is exposed to excessive heat. Larger compressors use high refrigerant pressure switches to prevent heat and high pressure damage to a system. Danfoss 12/24 volt compressors rely on abnormal high amperage generated by high liquid pressure to prevent compressor and its oil
from damaging heat.
compressor companies application engineers provide operating limits and approved refrigerants for each compressor. By reviewing Danfoss application performance specification sheets
it is easy to see operating limit conditions based on amperage, ambient standard day temperatures and a condenser hot gas temperature based on 55 C ( 131F ). Hot gas vapor/liquid leaving condenser temperatures on BD compressor systems for best performance will range from 105 Psi to 115 Psi with a condenser air cooling
medium temperature of 70 to 90 degrees F. These application sheets
set out process boundaries for watts of current
, amperage, and Btu output. If any one of the manufacturer’s performance limits is exceeded overall performance may be compromised as well as system’s extended reliability
. Danfoss makes no mention of condenser cooling
mediums other than convection air flow cooling condenser, compressor and electronic control module.
Operating temperature of a Danfoss BD compressor is controlled mainly by sub cooled refrigerant vapor returning from evaporator. Additional compressor cooling is provided by convection air flow directed across compressor’s thick steel
mass in warm climates. It is not unusual for compressor’s thick dome to reach 130 degrees F for short duration of 1 to 3 hours even when properly serviced with correct amount of refrigerant. There does not seem to be any quantifying data on returning gas vapor temperature needed to cool theses small BD compressors but 40 to 60 degrees F return gas vapor is desirable. In tropical climate temperatures I find 60 to 80 degrees F returning gas as a norm. Demands on compressor to remove heat from large boxes or for cooling low temperature freezers will reduce sub cooling of return gas vapor temperatures.
Most pleasure boat refrigerators powered by Danfoss BD compressors are air cooled and with the proper application design and installed correctly can provide 20 to 30 years of service
life. Contamination of refrigerants and extended operation of compressor at high temperatures are the only reasons I have found for Danfoss BD compressor failures.