Fact or fiction.... Not turning off A/C before ignition is bad......

And? Even if it does if u shut ac off it does not clear the system!!!!!!!!

 

Compressor head pressure is reduced when shutoff, the whole system equalizes to static pressure.

 

The voltage to the accessories drops because the starter is sucking it all up. At least in trucks with a acc/off/on switch and a separate button for the starter.

Now as far as these newfangled computer trucks, I know nothing except I'd be stupid to own one.

 

I don't see any issue on the mechanical side of things, but rather the electrical side. The clutch pack is activated by the voltage and you may never have a issue for many yrs. All you need is 1 good voltage spike and it can take out a capacitor or transistor. This is one reason you don't turn your lights on before starting your vehicle... it's just hard on the electrical. My CB, Stereo and a fw other items are wired directly to the batteries and I can watch these things power down for a moment when I start the truck. I got over 500,000 miles on my last AC compressor with original charge before the compressor went out.... I think I'd rather just be on the safe side and turn off the unit before starting the engine.
Really, what does it hurt to turn things off ?

 

we have had our truck since June of 2008 and up to 2 weeks ago never had a problem with the A/C, and we drove 450k miles over that period and never shut A/C down before we shut the truck off so I really see it as a old wives tale.

 

The real advantage to shutting the compressor off before shutting the engine down is to benefit the evaporator. When the A/C is running, the evaporator sweats. Shutting the truck down without giving the evaporator time to blow out and dry off with hot dry air can lead to mold growth and undesirable smells coming from the vents. If you shut the compressor off a few minutes before you kill the truck's ignition, it gives the fan time to remove some of the moisture that's built up on the evaporator.

The best thing you can do for your A/C is have the engine fan on when idling. It will prevent unnecessarily high head pressures in the compressor. Letting the fan cycle on and off results in a constant cycle of high then low head pressures.

 

I even heard it recommended to turn the hot water on and blow high speed for a few minutes before shutting down for the day to dry up the water on the evaporator.

 

That would depend on what side of the evap the heater is on. If it is after the evap, it wouldn't do any good.