# Good or bad (AC Split compressor input with cold freon)

Hermetic Compressor is used by split Air Conditioning unit. The compressor compressed freon gas coming from indoor unit. The gas is usually quite cold (about 2 deg.C lower than inside room temperature).

The question is: Is the compressor better inlet with cold or hot freon gas? What are the effects or reasoning?

I mean, would it be good that compressor gets cooling from cold freon but this might considered waste of freon work (add compression work because superheat condition)? The compressor cooling should be from outside. The next problem maybe if cold freon could cold the compressor oil.

If the compressor is designed to work with the fluid as a gas then the temperature is part of that design.

The gas entering the compressor is not primarily there for cooling - the primary function is for the cycle to move heat from one place (evaporator) to another (condenser).

• About the design, which considered better AC Split design? Compressor is off course always work with gas only, but between using freon as winding cooler or i.e use return gas to subcool outlet condenser, which is better? Yes, freon primary function is moving heat from evap to condenser. Commented Aug 11, 2017 at 1:22
• The compressor will compress the gas prior to running it through the condenser coil which will increase the temperature. This is necessary in order to shed the heat to the surrounding air, as the temperature of the compressed refrigerant needs to be hotter than the surrounding air for the heat to transfer. Commented Nov 17, 2017 at 5:01
• @Secundus yes. My question is after the hot freon goes to condenser, to TXV, to evaporator, freon gas will back to compressor. This incoming gas, will it better cool (no need excessive superheat) or hot (injected heat as much as we can)? Commented Dec 7, 2017 at 4:10

You can think of capacity of the total system as being proportional to the mass flow times the temperature jump the compressor puts on the refrigerant.

$$\dot Q \propto \dot{m}\cdot\left(T_{discharge}-T_{suction} \right)$$ or $$\dot Q = \epsilon \cdot k \cdot \dot{m}\cdot\left(T_{discharge}-T_{suction} \right)$$ If you keep everything else the same, and heat up the suction gas, then that heat has to be rejected by the system using the outdoor/condensing coil above and beyond the heat from the conditioned space, and above and beyond the heat from the compressor motor.

All things are not equal. This is an irony of science, we say ceteris paribus, but it never works out that way. If you change the suction line temperature, also called the evaporator temperature, then the compressor will try to make the discharge hotter.

So you could look at the "compressor equations" for your compressor and refrigerant in the operating envelope that operate on the evaporator(suction) and condenser (discharge) temperatures and give power, amps, mass flow, and capacity. These sorts of things should be published, public information.