Monitoring Air Conditioner Performance

We came home from vacation Sunday afternoon to a 100-degree heat wave. Although the air-conditioner was working well when we returned home, the house was hot Monday morning. Sense showed “other” rather than the Air conditioner running, and the condensate pump was not running. The fan in the compressor unit was running, the compressor unit was making noise, but it seems the compressor itself was not running. The vapor line of the compressor unit was not cold. I called for service, the technician arrived Tuesday night and I watched as he diagnosed the problem. Noticing how he used temperature and pressure readings to diagnose the unit gave me an idea. What if these key operating parameters could be monitored continuously?

A brief Internet search identified Alert Labs as active in this area. They offer an air-conditioning monitoring product and service called Sentree. See: I sent them an email asking if they have something more tailored to homeowners and integrated with Sense. They have not yet answered my query.

A simple system would monitor the temperature of the vapor and liquid connections at the compressor unit or the evaporator unit. A more complete system would also monitor pressure at those points and monitor ambient temperature, room temperature, and perhaps plenum temperatures. This could be integrated with sense monitoring to report electric usage per degree day, or per BTU of cooling. Such monitoring could also report changes that indicate early warning of refrigerant loss, or system efficiency reductions.

If anyone knows of such a system, or is developing such a system, please let us know.


I can’t help with your primary inquiry, but you may have caught this thread where I mentioned we’re digging into data of failed ACs to help with possible failure prediction in the future. Would you be OK with us looking at your data to see if we can spot the actual failure event?

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@lee this is the thread @RyanAtSense is referring to I believe

Regarding your other query … interesting! I see they were acquired by a much larger maintenance group.

More on the commercial side, I have used Monnit’s sensors to achieve similar things (leak detection; over-pressure; over/under-temp; high humidity etc … along with over-current; vibration and so on). They have been around a while and their products are quite “mature” at this point. They have saved my clients a lot, especially when you account for reduced insurance premiums. Sense can now directly manage some of that (over-current for example). Integration with Sense is still a kludge but there are good redundancy reasons to keep the systems entirely discrete (again, more on the commercial side, so I’m not really answering your question).

As far as I’m aware, btw, certain manufacturers of larger systems (Daikin, Mitsubishi [CityMulti] ) have directly accessible sensors that, if one “subscribes”, can be used for maintenance alerting. It’s easy to imagine that with the ubiquity and lowering costs of IoT & sensors that this will filter down to even the smallest systems … and fairly quickly.


Yes! Thanks.

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Excellent. Do you happen to know exactly what the tech diagnosed the problem as?

The failure occurred late July 21 or early July 22. He replaced the dual run capacitor (the likely problem) and also added 3 pounds of refrigerant (not clear if this was necessary) after 7 pm on July 23.

Hi Ryan,
I don’t know if your data science team wants to add another AC compressor death to the mix, but my downstairs compressor burned out (melted plug into going into the actual compressor unit) somewhere between June 11th and June 14th. My new (April 6th) Sense unit never detected the actual compressor before it failed, but the smartplug on my furnace gives some telltale signs of the failure. I think the AC compressor controller communication with the furnace controller blower fan supersedes the continuous cooling my downstairs Ecobee is calling for.


We definitely want to! I’ll pass it a long.

That sentree looks similar to a product I’ve seen in commercial space to monitor ultra low temp freezers, known as Traxx. It uses unit CT’s to monitor compressor amps, what for short cycling, and with that data uses predictive analysis to assess the condition of a freezer (compressor), instead of using actual pressure and refrigerant line temp sensors which could be problematic, not to mention expensive and not reliable over time.