Compressor over Heating

Is this a refigeration or A/C compressor or is it an air compressor ?

The simple answer is YES - (but not very helpful) - you simply ask the manufacturer of your (or any) compressor and they will tell you.

But if you want to know what temperature to expect from a compressor (without any data sheets or the manufacturer telling you) then a simple rule-of-thumb formula will point you in the right direction.

The formula comes from complex laws of thermodynamics. Briefly air heats up when rapidly compressed (adiabatic compression) - and depends on the starting temperature and working pressure. That if not cooled - the inlet air goes in hotter and hotter and the discharge air comes out hotter and hotter still. The effect is cumulative and rapid (minutes/hours rather than days or weeks). The compressor would overheat and suffer severe damage if not cooled (or stopped).

Cooling is therefore absolutely essential and your running temperature is therefore a function of how effective your cooling is. Small compressors for occasional use probably have simple radiator fins with air cooling - but continuously running and larger machines need forced air (fan) or water cooling (assuming plenty of cold air or water).

Back to the formula: Working with absolute pressure and temperature scales.

Td = Ti x R^0.286 (for air). Td = discharge temp. Ti = inlet temp

R = compression ratio = Pd/Pi = final discharge pressure divided by inlet pressure for a 1-stage machine.

For a 2-stage machine use ₂√R, for 3-stage use ₃√R, for n-stage use _n√R

The overall effect assumes perfect inter-cooling (the inlet temp to the 2nd/3rd/nth stage is the same as the inlet temp to the 1st stage.

If not then you need to take the outlet temperature of the 1st stage and use this as the inlet temperature of the 2nd stage - and so on to get the final discharge air temperature. This exercise will show the importance of inter-cooling

Oil flooded rotary screw compressors usually have one stage - thus can run that much hotter than the equivalent size multi-stage reciprocating compressor. However, the discharge temp of the screw is largely governed by how efficient the oil injection system is and that depends on how effective the oil cooling is.

Good luck

The equation, pv = nRT (for an ideal gas), tells you that temperature (absolute temperature) goes up linearly with pressure.

If your compressor's temperature is much higher than it should be, then it may be due to poor lubrication or high friction caused by poor lubrication.

Mr Ferreiro still has not told us what type of compressor(s) he's dealing with nor their application.

Refrigeration compressors have internal motors designed with little extra HP than what is needed to do their specific application under a realistic adverse condition. This is of course to boost efficiency. All motor amps are converted to heat which is transferred into the refrigerant.

Excessive heat due to excessive friction in the compressor itself means compressor "death" is emminent. Compressor's shutting down on internal overloads don't last AND it causes irreparable damage, scoring rings and cylinder walls, "cooking" copper windings, breaking down oils, warping heads and possibly damaging refrigerant itself.

Typically, compressor overheating happens from either excessive input heat from the evaporator side or more commonly a lack of heat rejection by the condensing circuit.

Compressor amp draw follows the amount of work it must do as well.

All manufacturer's publish the operating parameters of their equipment. The technician must determine which parameter is out of range.

Most refrigeration compressors require a properly charged and working system to provide proper cooling for the motor windings.

Hope this helps

Every compressor manufacturer is governed by the respective National / International Standards for the Compressors. As a guidline, for non-lubricated air-compressor, discharge air temperature from compressor flange is in the region of 400 degrees F, or lower preferred.

While for lubricated air-compressor, it is in the region of 350 degrees F. or less for getting a good trouble-free operation, in terms of hours of running etc.

I have assumed for air-compressors only here.

If we knew the application this would be easier.

Which part of the compressor temp would help too.

If, it is a lubricated type it has crankcase oil. Most oils have a recommend temp of 140F, Max. 180F. So if the crankcase oil temp exceeds these temps then any standard air compressor oil is on its way to failure.