A compressor is not necessarily a pump; it does move the vapor, but it also changes the volume, temperature, and pressure as it does so.

The refrigerant absorbs heat in the relatively cold evaporator coil, and it proceeds to the suction line. The suction line carries all of the heat in the home to the compressor, although you will feel just a cool vapor when you grab the suction line. That vapor will be very hot when it leaves the compressor.

In some cases, the cool vapor refrigerant goes into the head of the compressor from the larger suction line, where some of it cools the compressor. From there, the vapor undergoes compression and is pumped out of the compressor via the smaller discharge line.

You can think of a compressor as a room with a bunch of ping pong balls that keep bouncing. (The ping pong balls are molecules, and the speed at which they move is the temperature.) Those walls will start moving in, which moves against the force of the balls and causes them to bounce a lot faster. The molecular velocity increases, so the temperature increases. Although the compressor does generate some heat, most of the temperature increase inside the compressor can be attributed to the molecules being squeezed into a smaller space.

The gas laws also explain that; the temperature increases as the pressure increases, and they both decrease proportionally.