High liquid line temps

[JimD1]

A few of my co-workers are in a discussion about causes for a high liquid line temperatute og an A/C and or refrigeration system.

A few of the causes that they list that I don't argee with are :
1. Over charge
2. Bad Valves
3. Partially clogged cap tube or defective TXV

As for over charge, I am telling them that the LL temp will lower as you increase the charge in the system due to a slower velocity of the refrigerant in the causing more hang time in the condenser.

Any one agree or disagree?


Jim

 

[ProfSporlan]

Overcharging a system will increase condensing pressure and temperature, condenser TD, and subcooling, but it will not necessarily lower liquid temperature. Problem here is increased condenser temperature will typically outpace increased subcooling. I think you're confusing increased subcooling with lower liquid temperature.

The normal cause of a high liquid line temperature is a dirty condenser coil

 

[quark]

Prof is dead right as usual. Increasing charge will increase condensing pressure and temperature. Check the condenser coil. TXV has no effect on high temperature of liquid but to some extent yes, for low temperatures.

Regards,

 

[JimD1]

Yes, overcharging will increase the pressure and temperature to a point, but as you continue to overcharge the pressure will level off and the temperature on the liquidline will decrease and the superheat on your suction line will decrease until you flood back.

An overcharge will not necessarily cause a high LL temp. The way I was taught it that you will have a higher than usual LL temp during an undercharge with a TXV with a higher sub-cooling. As you add refrigerant the subcooling will decrease until you hit the mfg's recomendations. As you continue to add refrigerant ythe subcooling will continue to decrease.

Jim

 

[ProfSporlan]

I could buy into an argument that liquid line temperature would level off at some point when overcharging a system, provided you get floodback as a result. This would be expected with a system using a restrictor as an expansion device.

If the system used a TEV, however, one could expect it to control superheat, even if the system were substantially overcharged. In this case, condenser pressure and temperature would be expected to climb as we continue overcharging the system.

But at some point, even the compressor would lose enough capacity due to overcharging to limit condensing pressure and temperature, even if superheat were to be maintained. Here, I would expect to be at some nosebleed area above the high pressure cutout.