Here is what I believe is going on. The Chrysler V2 compressor takes power/ rpm's from the engine. That power robbed from the engine brings down your rpm's from where it normally is. The idle solenoid is supposed to kick up the idle, preventing the engine from stalling with the compressor running.
With that said, remember that when the compressor is doing it job, it is taking warm air from your passenger cabin, super heating it through the compressor and venting through the condensor, which is in front of your radiator. Now your engine needs to be cooled, but at idle it's not getting the benefit of large amounts of cool air being passed through both the radiator fins as well as the condensor fins, hence your temp gauge going up at idle.
When an engine gets warmer the lubricating oil tends to thin out and with the extra heat from the forementioned sources, you will get a lower reading on your oil guage as well as the fact that the engine is idling at a lower rpm and that means the oil pump is moving slower also since it's mechanically driven by the camshaft via the distributor drive gear.