HCFC and HFC mix. Whats the actual detriment?

[TheGinjaNinja]

Hey I'm still fairly new to the game so please pardon my ignorance, but I was wondering the other day, what is the actual detriment to a HCFC system (eg, R22) if a HFC refrigerant (eg, R404a) is used. I've heard all through my training that the two do not mix but no-one ever actually gave me a reason what happens and what the effect on the system is. If some one could give me an answer to this annoying burning question that would be great!

[Gary]

It forms a zeotropic mixture, where the refrigerants evaporate and condense at different temperatures. In extreme cases, one of the refrigerants may not be evaporating and/or condensing, making that portion of the charge ineffective.

IOW, it gives us... glide.