Please what is wrong with putting off your engine first before putting off the radio or AC. Does this damage the engine because my uncle always advises that I turn these off before putting off the engine and also if the radio is on, I must put the radio off before starting the car and then I can put it on. So what's your take on this?

princetunex:
Please what is wrong with putting off your engine first before putting off the radio or AC. Does this damage the engine because my uncle always advises that I turn these off before putting off the engine and also if the radio is on, I must put the radio off before starting the car and then I can put it on. So what's your take on this?

I don't think doing or not doing it has any effect on ur engine. Turning off ur engine while those are on simply means dt ur battery has to take over powering those things. Ur AC will not cool cos d battery cannot roll ur compressor. So if there's anything that will be affected, it should be ur battery, but then, that's why the battery is there, isn't it?
U should also know that starting ur engine while AC is on is not a good idea cos ur battery will need to turn ur engine together with d compressor. That's a lot of load for ur battery.
Car gurus can correct me if I'm wrong.

Macmilla:

I don't think doing or not doing it has any effect on ur engine. Turning off ur engine while those are on simply means dt ur battery has to take over powering those things. Ur AC will not cool cos d battery cannot roll ur compressor. So if there's anything that will be affected, it should be ur battery, but then, that's why the battery is there, isn't it?
U should also know that starting ur engine while AC is on is not a good idea cos ur battery will need to turn ur engine together with d compressor. That's a lot of load for ur battery.
Car gurus can correct me if I'm wrong.

Thanks sir. I understand better now at least.

Ok let me share my thought.

AC ON BEFORE ENGINE START
Like the person above have said, the AC compressor combined with the car engine forms a very big load on the starter motor and as well the battery, this reduces the lifespan of the starter motor because of the heat produced in the coils when trying to roll this big load. It also momentarily drags a very large current from the battery. So it is not a good practice in conventional cars.

However, this issue has been taking care of in some modern cars by disengaging the compressor clutch automatically when the engine is turned off and engaging it some seconds after the engine starts rolling.

RADIO ON BEFORE ENGINE START
In the case of radio, the problem is not heavy load on the starter motor or battery but electrical noise generated by the starter motor during cranking. Some cheap car audio system without proper power filtering responds to this electrical noise and it is capable of damaging components in the radio. It affects the radio mostly when the car battery is not good (those battery that drop to 8V during engine crank)

I DO NOT KNOW IT ALL. CORRECT ME WHERE I AM WRONG