Hello, I’m having a bit of a time getting the ADC T-3000 to work with my HVAC. I’m attaching a picture to show the existing wiring setup. Only 4 wires go to the T-3000: W, Y, G, and RH. In this config, the AC starts, runs for a minute, then stops and the display reads “System Protect” then starts counting down from 5 minutes.
If I wire the red lead into RC instead of RH, the panel can’t detect the wires properly. The docs say to use either RC or RH when your old t-stat had a jumper between the two. The docs say it doesn’t matter because they’re bridged internally. However, it definitely does matter in practice. Is my unit defective? Are the docs wrong? Should I be using RC instead of RH and just bypass the wiring detector?
System Protect is a 5-minute delay prior to calling for heating or cooling to protect the system from short cycling. It is only applied if the thermostat has detected an unexpected relay state internal to the thermostat during a call.
From ADC: “System Protect is intended to cover rare cases of power issues with the HVAC system. If System Protect is being seen frequently or appears on every call for heat or cool, it points to poor HVAC performance or pre-existing incompatibility. Frequent or extreme System Protect delays can be resolved by installing an isolation relay.”
You’ll need to install an isolation relay in this case. The T3000 terminals are digital relays rather than mechanical, and are very sensitive to excess current draw.
Thanks for the reply Jason. I did see that thread, but one thing has me bothered. The RC/RH behavior in my unit is really weird. The fact that it only works when connected to RH is bizarre. The docs very clearly state you can use either one…but in my case I can’t. That seems like a bug or something is defective.
I understand. It’s odd, however the T3000 is extremely sensitive to power changes. Wiring detection is a feature of its digital relays and only works properly when the expected electrical characteristics are present. If those are known to be an issue (they are in your case given the rest of the description), the results of the wiring detection are already suspect.
If you see system protect message frequently, it only means one thing, and an Isolation relay would be required in those cases.
Ah, if you were running off of battery then the Tstat would now be drawing power from that circuit as well. The relays are extremely sensitive, that may have had enough impact on the circuit to bring it within the expected parameters.
If you need of an isolation relay, these ISO series are designed for thermostats and much easier install than the one recommended by Alarm.com. They also give you isolation on all your thermostat signals, not just one.
