R-134a high side pressure drops to about 35 psi at 40*F, completely worthless to switch on that AC with defrost at these temperatures. Besides that PAG oil, women's facial cream is very stiff at these temperatures as is the compressor neoprene seal. All you are doing is wearing the darn thing out, really doesn't remove any moisture.
With other vehicles even mounted a switch in series with that AC compressor clutch coil, didn't do this with the Cruze, just cracked opened the driver's window to prevent fogging the windows, we are the culprits of this.
Was not a problem with Japanese made vehicles, 88 Supra is like this, when that AC switch is off, its off regardless if you hit defrost or not. Not sure about what the thinking is behind switching on the AC with defrost, but at about 34*F and below, R-134a pressure is so low, the thermistor keeps it off. It's that range from about 35 to 65*F is where it automatically switches on in defrost.
Yet another problem that is age old and never solved is debris buildup on the condenser, restricts air flow and high side pressures can of up to around 400 psi! Get very little cooling and really putting one heck of a load on that compressor, water pump is the weak link and the first thing to go in a single drive belt system. Really made life difficult to keep that condenser clean. If you think your windshield is loaded with bugs, look at your condenser.
Another is stone chips, quickly learned on my that little plastic stone shield was missing, dealer didn't believe this, several looked at it, ordered one for me, installed it myself. Front license plate required in my state was actually a blessing, has stone chips in it.
Wasn't much of a problem with tube and fin condensers, one solid piece of copper tubing ran back and forth with R-12, R-134a requires a parallel flow condenser made out of super thin aluminum and is throwaway. R-134a PAG oil is hygroscopic and with moisture forms sludge that can plug up the orifice. Should be completely flushed, deep vacuum drawn, and PAG oil injected in to do the job right. Mineral oil never had this problem.
Yet another problem is that the EPA changed the service ports to a quick coupler from the old reliable Scharder valve, so you could not pour R-12 into these systems, have a tool that let me replace a 50 cent valve without discharging the system, now you have to replace the entire line with a leaking port. Uses a large disc that never seats properly that causes leaks, and while R-12 had a metal cap for the service ports, R-134a switched to plastic.
CFC's were blamed for ozone depletion, but yet 95% of the total CFC production was never used for its intended purpose, all open spraying for spray cans and cleaning, less than 5% was used for refrigeration! And unlike leaded gas that was really a health hazard with a 20 year phase out, CFC's were banned overnight. And the manufacturers of CFC's were not held responsible, but up to the consumer to pay for the conversions.
DuPont came along with R-134a, now being blamed for global warming and while the EPA banned trichloroethylene back in around 1974 as being extremely dangerous, gave DuPont permission to use it for the production of R-134a.
Just a few bit of hard core facts why we are having problems and very expensive ones at that.