TLDR: The fins of the condenser (external unit of the air conditioner) were blocked with grime and grease and have been cleaned. Also the A/C has been struggling to cool and dehumidify the volume of air in TAMI. Cleaning the condenser should help restore some of the cooling capacity.
The before, behold the horror
Condenser coil blocked (the outdoor unit)
Evaporator coil (the indoor unit)
Power consumption , Before and After cleaning the condenser
YF with assitance of JR decided to clean the aircon filter and condenser/radiator coils (and evap coils while we're at it). By counting secs/rev for the electrics when all fuses were off but for the aircon, aircon electric usage can be estimated rather exactly (0.1W !?!?) with multiple secs/rev measurements , assuming 80revs/kWh. As indicated by the slope of the graphs below (of Kwh/h) , we dropped from 4.90KW to 4.67KW or 230W , not bad for spraying down some coils with water and detergent.
The after cleaning the condenser and the evaporator
The saga continues! Emptied one of the cans, but the other doesn't foam.
1. The air conditioner is a heat pump that absorbs heat from inside TAMI and transfers it to the outside by investing work (compression).
2. The amount of heat rejected by the outdoor unit is the amount of heat absorbed by the indoor unit + heat gain from compression losses.
3. The rate of heat transfer is proportional to airflow, surface area and delta T between the coil and the incoming air.
4. When the condenser surface is blocked, there is less airflow. This means that in order to remove the same amount of heat the delta T must be higher.
5. Higher delta T is essentially achieved through a higher condensation temperature, and pressure. A higher condensation pressure reduces the efficiency of the compressor since the volume losses contain a higher mass of refrigerant at higher pressure. So overtime to remove the same amount of heat, more work is required (and the electricity bill with it).
6. Furthermore, the compressor has a limited capacity to provide a delta P between the suction and the discharge, so if the condensation pressure increases, so does the suction pressure.
7. With increasing suction pressure, the temperature of the coil of the indoor unit also increase, there is less removal of humidity from the air (which you may have already felt this past summer ('19)).