I've been in the AC business for a short time and have solved most problems I've come across. This one is bugging me, though.
3.5 ton Rheem Corsaire R-22 (yeah, I know, cheap), condensing unit < 2 years old with a Ruud air handler - fixed orifice. The system worked fine until about a month ago when the temp in the house would no longer go below 76-77'F. The gage readings fluctuate between 230 and 300 high side and 58-67 low side. The readings fluctuate at a regular interval, i.e. high side goes low, then low side goes low, high side goes back up, then low side goes up. This repeats approx. 2-3 per minute. I checked the orifice - no clog. Temp difference across filter dryer is 0'F.