Help me understand these four components in a PCB (I'm a novice)

Question

I removed my A/C split 9000 but pcb (indoor unit).

There are some components I cannot identify or fully recognize at all.

1. The blue box with a little plastic bag. What's that? and what's for the bag? (isolation)?
2. Is it a resistor or inductor. When I measured it I believed it was more than 16 MΩ.
3. The green items seem like a capacitor? Thermistor?
4. I know it's a resistor: 39 kΩ, BUT How can I tell the watts tolerance? I know it depends on the thickness of its body, however there are newer resistors slimmer with higher watt resistance.

Answer 1

1. A transformer that forms part of a switching power supply. It does provide galvanic isolation. The brains of the outfit is the Matsushita MIP2F2, with some help from IC201 through an optoisolator.

2. Looks like 22MΩ 5% resistors, probably rated for mains voltage + surge and the construction and black band suggests some safety characteristics suitable for direct mains connection.

3. They are NTC thermistors used for preventing turn-on surge. They will measure low resistance and drop as they heat up. Looks like two in parallel (or one in each leg, so effectively in series).

4. 39kΩ resistors.

The lack of fireworks byproducts suggests that the Panasonic chip may still be functional.

Answer 2

1. mainns transformer for switch mode power supply. Wrapped in insulating tape to protect the windings, and for extra insulation.

2. Resistor. 22 Mohm, 5% tolerance, likely a special fusible resistor.

3. Likely a NTC thermistor for limiting short-term inrush current when plugging in the mains plug, or PTC thermistor for protecting from longer term overload or fault current.

4. Correct, 39 kohm resistor. Wattage is unknown as it cannot be identified.

Answer 3

You can tell a lot by looking at the lettering - the stencils - on the printed circuit board (PCB).

Item 1 I'm guessing is a transformer. The plastic provides insulation from the metal of the transformer. Also, I would expect a transformer and some sort of low voltage power supply to provide the lower DC voltage needed by the control electronics. It could also be a big power contactor (relay).

Item 2 is a resistor. Note the R designation next to it and a similar component, R331, just to the right of the one you boxed in.

Item 3 looks like it may be a disc thermistor, from the TH designation. From looking at it, I would have guessed a disc capacitor, but that doesn't go with the reference designator on the board. For an example of the latter look at the lighter green disc parts where your thumb is. These are capacitors.

Item 4 is a resistor, as you guessed. The tolerance is given by one of the colored bands.

Note, diodes are usually delineated by CR, or D, as in CR101 or D101.

Answer 4

1. Is a transformer. Seeing the optocoupler next to it, this is probably a regulated isolated power supply based on rapidly switching the current through a high-frequency transformer on and off.
2. Can't really tell, your colored box cuts through the position of the silkscreen that would have told me. If it says "R" followed by a number, a resistor. If it says "L" followed by a number, an inductor. More likely to be a resistor, though!
3. That's probably a varistor or thermistor
4. same as 2, resistor. Tolerance would be a separate stripe. If stripe is missing, assume 20%. The relevant thing here seems to be more the heat power capacity than precision.