Unfortunately I have a vivid memory of the opposite: driving an extremely decrepit old car through the south in July, had to crank the heat to max to try to direct the heat away from the engine. No AC in the car, naturally.
I also have this memory. The A/C is a heat pump that just pulled heat to/from the radiator, which is used for both the engine and the A/C. So turning on the heat causes the thermostat to be tripped faster (or so I was told), moving heat away from the engine. You had to be moving for this to work well, especially if your thermostat was going bad.