As illustrated above, his air conditioners are the packaged type that is installed through a wall or window. Such unit is designed to cool a single room.
There were two units with similar problems. The first one I looked at is an old Made-in-China no-name unit, with a cooling capacity of 12000 BTU and uses R-22 refrigerant. The unit runs, but the user complained about compressor shutdown during hot days. On those days, the unit would start up fine and output cool air. Yet, sometime after start, the unit would not cool anymore (but the fan continues to run). If the outside temperature drops, the unit would be back to normal operation on its own.
I was also told that the drain has blocked recently. The user was able to fix that himself. A part of the fix, he rinsed the condenser coils with soap and water. Such testimony led me to believe that airflow restriction due to condenser coil blockage is the cause.
Enough speculating - It's time to take a closer look at the unit. Before I continue, here is a friendly WARNING to viewers who wishes to try repairing their home appliances. Please read the disclaimer on this website. Most home appliances run on line voltage that can serious hurt or kill you. ALWAYS disconnect power before working on the appliance. The unit was unplugged during the whole repair process. If the appliance you need to work on is permanently attached to a connection unit on the wall (e.g. bathroom extractor fan), you have to switch off the power at the circuit breaker first. You should then confirm that the power is indeed off at the connection unit, as it's always possible to switch off the wrong breaker. As always, do NOT attempt the repair unless you absolutely 100% understand what you are doing and what the risks are.
Obviously, the front cover had to be removed:
Like I mentioned earlier, this is an old unit. The dust and stain shown are typical. The power cable is routed to where the controls are, so there must be something behind the knobs.
There we go. Since the unit utilized non-electronic control, the troubleshooting process was really simple. In fact, the potential culprits are in plain sight - capacitors. The large rusted can (CBB65) is a run capacitor for the compressor, while the black rectangular one (CBB61) is a run capacitor for the fan motor.
CBB65, label = 35 micro-farad ± 5% (33.25 - 36.75)
CBB65, meter = 34.9 micro-farad (0.3% less than labelled value)
CBB61, label = 3 micro-farad ± 5% (2.85 - 3.15)
CBB61, meter = 2.44 micro-farad (19% less than labelled value)
Just as I suspected, the run capacitor for the fan motor is the fault. With a faulty capacitor, the fan runs at reduced speed. This reduced cooling efficiency of the condenser coil to the point that the compressor overheats and triggers the automatic thermal overload shut-off.
Typically, if the meter reading is within 10% then the capacitor is still considered acceptable. The CBB61 here is definitely not. The only method of repair is to replace the faulty capacitor with a new one.
With this unit fixed, it is time to move on to another one with similar but more severe problems. Again, I began by removing the front cover:
This is yet another old Made-in-China no-name unit, with a cooling capacity of 7500 BTU and uses R-22 refrigerant. The unit would hum/buzz when powered on. Since this unit was located in a bedroom, the user rarely uses it due to the noise.
Hum/buzz is a common symptom of a dying capacitor on an electric motor, so I knew this would be another quick one.
The design is common among units with non-electronic control. The large blue can (CBB65) is a run capacitor for the compressor, while the black rectangular one (CBB61) is a run capacitor for the fan motor.
CBB65, label = 17 micro-farad ± 5% (16.15 - 17.85)
CBB65, meter = 16.8 micro-farad (1% less than labelled value)
CBB61, label = 3 micro-farad ± 5% (2.85 - 3.15)
CBB61, meter = 0.737 micro-farad (75% less than labelled value)
Although the multimeter I used was a trustworthy Fluke 87-5, I still couldn't believe the reading at the first test of the CBB61. No wonder the fan motor would hum/buzz like no tomorrow! Just like the previous case, the only method of repair is to replace the faulty capacitor with a new one.
Speaking of the new capacitor:
All the specifications (capacitance, voltage rating, operation temperature rating) of the new one are identical to those on the faulty one.
It is worth noting that, after the capacitor replacement, both units not only work normally, but also blow much stronger stream of air.
