Another interesting thing in the aluminum cleaning threads about cleaning aluminum trim, PB Blaster was said to do some chemical cleaning on aluminum. If you have a really crappy looking condenser it may be worth searching and reading about it. A two step cleaning of something like PB Blaster and an aluminum cleaner may do wonders.

Refrigeration shops sell chemical cleaners for condenser and evaporator coils, I would have gone this route if I wasn't working on my salted road beater and really short on time.

A clean evaporator would be just as important for efficiency and is aluminum also. I hate working under the dash though - maybe next year.

Condenser cleaning will be a yearly ritual for me. An invisible layer of road grime seems to be good for at least a few degrees of cooling from the vents.

I will be keeping an eye on this, my results almost seem too good to be true. A look at a buddy's SnapOn AC manual gave me a chart relating low side pressures to evaporator temps. That is where I came up with the 28psi low side for max cooling with 134a.