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High pressure side general

mckpaul on Wed October 17, 2007 2:56 PM User is offlineView users profile

Year: 1984
Make: Chevy
Model: C-10 Pickup
Engine Size: 305
Refrigerant Type: R134a

In the high pressure path..compressor-condenser-evaporator...assuming everything is in proper working order, is the gas pressure in the line between the compressor and condenser the same as the liquid pressure in the line between the condenser and evaporator? (well, before the oriface tube anyway) I realize they fluxuate some with temperature changes etc, but how close are they to each other and do they follow each other closely when they change? Seems like the gas side would be able to change faster (say for example if the compressor turned off) than the liquid side.


Edited: Wed October 17, 2007 at 2:56 PM by mckpaul

TRB on Thu October 18, 2007 12:37 AM User is offlineView users profile

I do believe your discharge pressure (comp to cond) is going to be higher than the liquid pressure (bottom cond to drier or inlet evap). I have never measure this but that's my thinking. I'll let the engineers get into all the finer details.


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NickD on Thu October 18, 2007 9:46 AM User is offline

Basics of fluid pressure drops depends upon the length, cross sectional area, and number and type of curves in the media carrying the fluid. Plus in an AC system the condenser converts hot gas into a much cooler fluid, so yes, there are considerable pressure drops between the outlet of the compressor and the condenser. How much? Depends on system design, engineering books on this subject have equations. Also, the outlet of the compressor is not constant, but a series of very high pressure pulses that the condenser tends to dampen out. Gauges read average pressure that is much lower. National Semiconductor and others make electronic pressure sensors that respond to these pulses and can be viewed on a calibrated oscilloscope.

Everything is a lot more complicated than what meets the eye.

mk378 on Thu October 18, 2007 12:01 PM User is offline

The difference will be slight, and it is mostly because every component has a certain pressure drop proportional to the flow thru it. When the compressor stops, flow stops for the most part as well, so I would expect the pressure to be almost exactly equal then.

Pressure in a quantity of liquid can change almost instantaneously because liquid is not compressible. In gas, pressure tends to change more gradually.

mckpaul on Thu October 18, 2007 2:08 PM User is offlineView users profile

Cool, thanks guys. Still playing with what to do with this old truck while I have it all opened up along the lines of creating a spot to add a switch for a condenser fan if needed later on. Not adding the switch, just a schrader valve port for one for easy access later, would make it easier to add or change to a higher or lower level switch without rechanging. Ran across a #8 to #8 inline adapter that would add a port at the inlet to the condenser, but then wondered if a switch would be happy and work right looking at gas as opposed to liquid. May not even need it, and if not, no great loss, and I end up with an extra high pressure port. But we do have some pretty hot times here in the summer.

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