Well, I am in sunny 95 degree weather here in east Tennessee. Thermostat set at 78 and keeping cool. True that latter in the day when it really heats up, the compressors do not cycle and the temp may rise to 79. This means the compressors are constantly working and pumping out air that is about 65 degrees. Since we have overhead ducts they are constantly blowing all that cold air on my head. Have to wear a cap inside.
A problem you may be having is a separation in the duct that runs up from the unit to where it splits into a Y to feed the two ducts running the length of the MH>. This has been a know issue. In fact, It happen to mine after about 2 years.
Another possible is that #2 may not be coming on. #1 comes on first, then #2. To check, Trip the breaker on #2. Turn on the system and let run for a few minutes. Then turn on #2. You should be hear it turn on. Another way to test would be to plug into a 30 amp circuit. Turn #2 of and read the amps, Then turn on #2 and see if the load increases. This will tell if #2 is working.
Other that getting a tech to come out, that all I know to suggest.