Since sealed units dont have a service port for gauges it makes checking to see if it is low on refrigerant not a quick as with other HVAC systems.
Installing service ports can be done and is not a difficult job but some basic things can be done first.
Using an Amp meter and a IR temperature gun we can quickly tell if there is no refrigerant flowing inside a sealed system.
Method #1 Use an Amp Meter
Most small compressors installed in window units or similar will run around 2 Amps. Of course, check the face-plate to be sure what amps it uses.
If the compressor is not working and pumping refrigerant in the system the amps will be much lower compared to the standard amps.
For example, a compressor that regularly uses 2 Amps will be using 1 Amp or lower.
Of course, the compressor doesn’t always run and shuts off and on, so be sure the temperature is set lower for the unit to kick on.
If the amps are low it does not automatically make the compressor bad but does point the the fact that refrigerant is not flowing in the system for what ever reason.
Most condensers will run around 100 degrees so if it is low than you will know there is a problem.
Of course, be sure the condensing fan motor is running pushing air through the coils and dissipating the hot air.
The above method are just some simple things to quickly check when you approach a sealed HVAC system and want to see if there is refrigerant flowing.
There is no doubt many other methods that can be used to troubleshoot a unit.
Somethings will even be obvious such as the noise the compressor is making on the window unit.
If in doubt installing a service port to hook up gauges is an easy job with the right equipment and can be done easily.
Read Here for how to install a service port on a small window A/C unit.