Causes of Negative Subcooling

[HVACR_CA]

First of all, is it possible to have negative subcooling (ie liquid line temp is greater than temp of condensation)? Second, what could cause this to happen?

[INTECHBILL]

This happens whenever the compressor absorbs heat instead of rejecting it ! Many causes ! Read the book ..

[JStar]

Undercharged? Dirty condenser fins?

[beenthere]

This happens whenever the compressor absorbs heat instead of rejecting it ! Many causes ! Read the book ..

The compressor doesn't reject heat. It just moves vapor.

The condenser coil rejects heat.


OP. Check your gauges and temp meter.

[INTECHBILL]

The compressor doesn't reject heat. It just moves vapor.

The condenser coil rejects heat.


OP. Check your gauges and temp meter.

expl # 1

If I'm not mistaken if the compressor is loaded with oil , the oil will hold heat and there you have it yes?

Expl #2

If the outdoor coil is restricted the compressor will overheat - yes ?

Expl # 3

many of my medium and Low temp application compressors move some liquid for proper S/c / S/h - yes ?

NEXT !

[beenthere]

But its still not the compressor that rejects heat. It only moves the vapor. Its u to the condenser to remove the heat of the vapor/hot gas discharge.

The return gas is what cools the compressor by absorbing heat from the compressor.

If the compressor is loaded with oil. You have another problem.
The condenser has to be more then restricted to cause a compressor to shut down on its IP. If the condenser fan is not working. Then its the condenser coil that is not removing heat.
Most medium temp compressors don't need liquid returning to them to remain cool.
But if they do. Then it is the refrigerant that is absorbing heat from the compressor. Not the compressor rejecting heat.

[jpsmith1cm]

expl # 1

If I'm not mistaken if the compressor is loaded with oil , the oil will hold heat and there you have it yes?

Expl #2

If the outdoor coil is restricted the compressor will overheat - yes ?

Expl # 3

many of my medium and Low temp application compressors move some liquid for proper S/c / S/h - yes ?

NEXT !

HUH?

If the compressor is loaded with oil, you got a problem. FIX IT!

If the outdoor coil is restricted, you got a problem. FIX IT!

In NO application should liquid return to the compressor. NONE! Liquid is hard on pumps.

BT is right. The compressor neither absorbs nor rejects heat, only moves vapor.

Maybe you ought to

[INTECHBILL]

HUH?

If the compressor is loaded with oil, you got a problem. FIX IT!

If the outdoor coil is restricted, you got a problem. FIX IT!

In NO application should liquid return to the compressor. NONE! Liquid is hard on pumps.

BT is right. The compressor neither absorbs nor rejects heat, only moves vapor.

Maybe you ought to

Have you not worked on Semi-Hermetic Low Temp Commercial applications -- If the compressor creates heat by "heat of compression" and can't get rid of the heat -- then what happens ! OHHH ! Just the other day a contractor called me to an ice cream plant & the compressor was operating under normal conditions pumping a liitle liquid .. & Of course I understand the basic principles of refrigeration -- you probably have worked on some equipment that was designed by yours truly !!

[ticotech cayman]

INTECBILL; IF the condenser is restricted the high pressure 'll increaes as well the compressor amps drawing , due to that , the widing temp 'll raise and the compressor overheats , but that does'nt mean than the compressor adsorbs heat. Anyways I think it could happen if the condenser coil is away too big, I had a similar situation with a chiller, the unit was a litte low in refregerant and the discharge line was conected to a heatexchanger to heat the water, so was over sodcooling the refregerant so at the end of the condenser the liquid line was aCtually cold and sweating.

[INTECHBILL]

INTECBILL; IF the condenser is restricted the high pressure 'll increaes as well the compressor amps drawing , due to that , the widing temp 'll raise and the compressor overheats , but that does'nt mean than the compressor adsorbs heat. Anyways I think it could happen if the condenser coil is away too big, I had a similar situation with a chiller, the unit was a litte low in refregerant and the discharge line was conected to a heatexchanger to heat the water, so was over sodcooling the refregerant so at the end of the condenser the liquid line was atually cold and sweating.

Thats right many things can happen related to sub-cool & super-heat , if you fully understand heat principles .., even you release heat / over 80% on top of your head ... Then why the compressor wont release any heat --- Put your hand on it ! Touch it ! Of course if releases some heat bUTTT not as a component !

[bornriding]

First of all, is it possible to have negative subcooling (ie liquid line temp is greater than temp of condensation)? Second, what could cause this to happen?

The answer is basically...NO
The saturated temp of the refrigerant MUST be higher than the surrounding air ( air cooled ). If any heat is rejected so that the vapor condenses, then the temp of the liquid in the liquid line COULD NOT be greater than it started with, because it would be higher than the ambient which isthe only place the liquid could possibly absorb heat from...
Even if no condensing were taking place, besides high head pressures, the vapor in the liquid line would still be rejecting heat to the ambient.

Richard

[jpsmith1cm]

This happens whenever the compressor absorbs heat instead of rejecting it ! Many causes ! Read the book ..

I keep coming back to this statement.

Can you elaborate on how this causes problems condensing?

[allan38]

Check your gauges and thermometers. You can have all kinds of funny conclusions when your instruments are damaged.

The system either isn't condensing or is condensing at a pressure much lower than you think. Such as wrong refrigerant, R-22 instead of R-410a. Some jackleg filled an R-22 system with R-12. Nahhh.... not likely.

I'd check my gauges first and avoid looking like a fool. Then the thermometer.