If you park your vehicle with a soaking wet evaporator in particular in a warm climate climate, nature will take over for developing mold. Not a new problem, started way back in the 50's when AC first became popular. Was a 1939 Packard as the very first vehicle that had AC.
Only way to prevent this is to switch the compressor off, my rule is about five minutes to leave the blower motor run at full blast before parking your vehicle. And have been doing this in the early 60's without any mold problems.
But mold problems is just the start of your problems, will also have corrosion problems. $$$$$ is the only result of these.
When automatic climate control first came out in around the early 60's, did not have a so called "Econ" mode, all it would do is switch off the compressor. So on these, mounted a rocker switch under the lower dash in series with the compressor clutch solenoid so I could switch it off. Didn't have to do with when they finally added on the Econ switch.
GM is very well aware of this problem, on just a hand full of vehicles, added a timer to keep the blower motor running for about five minutes after the ignition was switched off.
What is really downright stupid is switching on the AC with Defrost, at these colder temperatures, the moisture is very low, and switching on the compressor with a very cold compressor seal that is stiff, so you would lose refrigerant. Idiots that designed the Cruze did this exact same thing, even though they added a compressor switch. You can see that green light come on, but only when the ambient temperature is above about 34*F.
Not quite as bad with the V-5 compressor as it runs all the time, but when the cycling system was used, another POS, compressor would cycle on and off continuously accelerating from zero to the engine speed putting huge unnecessary stress on the belt drive system wearing it out with very little affect on defrosting your windshield.
On previous vehicles using a real mode switch, could cut the wire off that runs the compressor, but can't do this on the Cruze without having the source code on the BCM. So I just crack open a window the defrost the windshield almost instantly. Below 34*F, no problem, a thermistor keeps the compressor off.
Yet another problem finally solved with the Cruze is adding a cabin filter. Would describe the squirrel cage blower wheel as a leaf chopper that would pile up debris on the face of the evaporator and plug the drain hose. In these cases, the evaporator is sitting in a pool of water. Normally just removing the blower motor would give access to the evaporator so you could clean it out.
Slightly off topic, but can have the same exact problem with the HVAC system in your home, when the AC kicks off, so does the blower leaving the evaporator soaking wet for mold buildup. Solved this by modifying the furnace so the blower is always running at a low speed. Not only prevents mold buildup on the evaporator, but the entire house as well. Did this back in 1965 with my first HVAC system installation. With my newest furnace, low speed was running too high, so designed a motor control circuit to slow it down. Also keeps your home with a much fresher odor.
This is what is called common sense, that is becoming rare nowadays. And since that motor is always running, its the start up that really wears them out. Still kept my 30 year old blower motor, and still runs and looks like new.
