Why does the engen bog down when you turn on the heat of air conditioner?

Hello, the air conditioning compressor will turn on for heat or air conditioning both. This component kicking on indeed will create a heavy load on the engine. But it should not make a terribly noticeable difference. If it does, the compressor itself may be experiencing internal wear causing excessive resistance turning, or more likely, you could have an engine performance problem that is accentuated by turning the compressor on. Testing hands on is needed.

Normal operation.