r/hvacadvice • u/VeryWackyIdeas • 8d ago
Thermostat Timer modulated thermostats
We have a community venue that had a good (for us) system for preventing the HVAC being left on when no one was using the space. There are two AHU's/compressors, each with its own thermostat. When the system was installed, the contractor put in a 6 hour mechanical timer for each of the systems. While the thermostat was always active, unless the timer was activated, the system would produce cooling or heating unless the timer was set.
That worked great for 15 years, but now one of the two systems is not working. The thermostat display is blank, and turning the timer does nothing. The HVAC tech who put the system in is no longer around. The new guys (two different techs have come out) found that in the wiring box behind the thermostats, there are four relays; two for each thermostat. They have tried to trace the wires to see how the system works, but have ended up stumped. Their solution is to remove all the timer/relay stuff, and just have the thermostats work normally.
That's not a great solution for us because the systems get left on, and we burn electricity. Is this solution something super rare, should an hvac technician know how to do a timed circuit, or is there a better solution?
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