You might want to check with some other HVAC guys. I was told to keep it under 180 degrees of you can degrade the freon. I don't know if that's true or not. I should research that some more.
I have never seen any information that freon can degrade in any form or fashion. There are 3 things that can happen to "freon". 1. It can leak out 2. If it's a blend and you have a small leak it can fractionize (blends are made up of several different refrigerants and they all have a specific glide factor thus they leak at diff rates) 3. When "freon" comes into contact with air then acid forms.
The only thing you need to be concerned with in cleaning coils is the temperature. "Freon" has a direct relationship with pressure/temperature. I looked on my chart and it only goes to 155*F which would produce 405 psi with R-22. At 200 plus degrees you could be creating a pressure which could cause a rupture someplace in the high side of the system. In most cases this would be the compressor shell (depending on what type of system you are working on). Worst case sceneriao is you will severely damage the equipment. The other risk you are running is systems that have a high side manual reset. You turn the unit back on after cleaning and nothing happens. There are not a ton of those systems out there as manufactures are cheap and don't install this cheap part although im sure most of the R410 units will come with them as we transition from R22 to 410a.
HVAC is like all other trades when it comes to hacks. If you are dealing with a system that has been exposed to air in the system and acid has formed and been running forever then the integrity of the copper will be very degraded. I had a walk in cooler that had some holes in the u-bends of the evap and when I put my finger up there to feel the air, the entire u-bend crumbled under light pressure from my touch. I tested this system and it was one of the highest concentrations of acid that I have ever seen!
I did see an article one time in a HVAC magazine that showed this guy going around to motels across the country and "steam" cleaning the coils. It was talking about how this would kill any germs/bacteria that may be living in these unscrupulous places and how steam cleaning would kill those germs and get the coils sparkling clean. This can be something that anyone in the states should be able to do since these units are "self contained". They are basically window units and you can even service them in most cases unless your state catches you with the "commercial" clause which would result in a licensed blah blah blah to do the job.
And yes Tony I have a license to Chill...even freeze...but my license to cool is still waiting on me to take that test. I guess I better get that done in the next month or so....before the Texas heat wave gets here anyway.
Bottom line is let the chemicals do the work that you need them to do and be careful even using a water hose to rinse with as you can damage coils by looking at them wrong.