Some one has blocked the two hoses at the rear of the heads.
Pull the one nearest the monovalve,jam a garden hose down it so it pushes water into the engine,with the radiator cap off. No flow means it has been blocked to fix a heater that wouldn't shut off.
Theres is also every chance that the spigots on the heads are corroded up.
it also sounds as though your compressor is not shutting off pointing to either one of the control solenoids hooked up incorrectly or the dial control needing a bit of attention.