A/C differential temperature?

[toocoys]

What is "differential temperature"?

The aft air conditioner has great overboard discharge pressure, however, the differential temperature is less than 10 degrees. Recommend servicing the aft air conditioner.

 

[caltexflanc]

The difference in air temp before it enters in the return vent and when it exits the outlet vent.

 

[toocoys]

ah. So maybe just freon or something needed.

 

[Maerin]

ah. So maybe just freon or something needed.

Maybe it just needs service.

There's a very common misconception that "adding freon" is a normal part of A/C service. It is not. A service tech who indicates "it was just low on charge" on his way out raises red flags for a number of reasons. Most concerning is that a normally functioning system will not need the refrigerant charge adjusted- unless... 1) there is a leak. That can be an indicator of a bigger problem, and adding charge is not a diagnosis or a repair, it's a band aid. A leak requires a repair. 2) the tech who worked on it before was short on his skillset and adjusted the charge because... uh... just because.

Putting a gauge set on an A/C system can be part of good DX procedure, but it's not necessarily to adjust refrigerant levels. It shows system operating pressures and gives an indication of how the system is functioning. If your system is experiencing low splits, check for air flow, check for poor transfer on the seawater exchanger. You could conceiveably have good flow with poor transfer, and system pressures would point to that. So don't automatically jump to the refrigerant without a thorough and logical troubleshooting process.