Failing Air Conditioner, ISY944i, and Nest thermostat

[m_theredhead]

Hello All,

 

I am having an issue with my AC unit where the compressor isn't always coming on.   This usually manifests itself by the thermostat showing the AC unit is running, but the temperature in the house is rising or at least isn't cooling off.

 

I have an isy994i and a nest thermostat.

 

I was hoping I could have the isy ping the nest periodically ( every 5 minutes? ), get the current temperature the nest is set to cool to and what is the current temperature in the house.   If the difference is more than ~5 degrees, text me to alert of an issue.

 

Looking through the forum, it appears there are some challenges with integrating with the nest.   Does anyone have a script or some examples that I could start with to accomplish this goal?

 

This was pretty easy to set up with ifttt, but I prefer not relying on cloud based services for HA logic.  The nest app supports this concept, but they won't alert you unless the temp goes over 95 degrees.

 

Thoughts?

[paulbates]

Hi

Some things to consider:

 

AC not running when its called:

• Some power companies provide interrupt-able power service at a reduced cost. I have this. When an particular grid has a peak power demand, they have the right to remotely cut your air off (usually a few times a season max). You would probably know that you have this feature, usually there are 2 meters and two entries on the bil, but the symptoms that you are documenting support this hypothesis
   
•  AC systems can have an X minute safeguard built in so they don't run continuously. This is also an explanation for your symptoms, especially if its leaked coolant and working harder than normal.

Nest:

The Nest is a cloud only API; a cloud service is called no matter what mechanism you choose to integrate it with. Solutions that integrate the Nest with the ISY require a system-in-the-middle that can run python. There is a python based Nest app for the ISY's Polyglot framework. I believe most users have RaspberryPi (or equivalent) computer in the middle:

 

ISY <-> Polyglot (on Pi) <-> Nest Cloud API

 

Paul

[stusviews]

Are you using the ISY to control the thermostat. If so, then what's the result if you adjust the thermostat manually or depend entirely on the Nest's ability to automatically control the AC?

[m_theredhead]

Stu, I am not using the ISY to control the thermostat at this time.  I am only wanting to query it at the moment.

 

I would of course have to account for things like away/coming home, etc in the calculation.  This should be easy to do by tracking the last polled set value versus the current polled value and if different, adjust the allowed differrence for a period of time before alerting.

[m_theredhead]

Hi Paul,

 

Thanks for the response.  

 

My power company is not one that has the ability/right to remotely cut my air.   

 

I have had my AC guy out here 4-5 times already this season and the issue is intermittent and doesn't usually happen at a time with high capacity usage (afternoon).   Coolant is good and everything else checks out.   I am not really looking at using notifications for anything other than pin pointing when the issue starts so I can ultimately get this fixed permanently.

 

I will look into the cloud api solution you mentioned.   I thought there was a way to query the nest locally and not go through the cloud service.  That is unfortunate that it can not.   I have a Linux server at home  that is on 24/7 anyway so it may be easier just to look at running something there and not messing with the isy at all.   

[larryllix]

Do you have a Nest thermostat installed without the "C" wire?

[paulbates]

The advantages of putting polyglot on the unix box and connecting the ISY are:

• Integration with other things... If someone opens our family room doorwall, after x minutes the thermostats are set to off and the attic dampers are opened. Or if the attic fan is turned on.. dampers opened, HVAC systems set to off. I also cancel HVAC fan cycling during those events. Also, a keypad key sets "away" mode for the house, that includes HVAC and other things.
   
• Integrated notifications. I have the ISY send pushover notifications, and HVAC activities is one pushover "app" as well as sprinklers, garage door, etc

Paul

[m_theredhead]

Hi  Larryllix,

 

I do have a C wire.   I actually have two identical units with nest thermostats and they have run fine for several years, so I don't think there is a general configuration issue.

 

 

While looking for solutions, I found an ifttt applet that already does what I wanted.  It took like 2 minutes to set up to provide the alerting I needed.

 

I will still look into further integration with polyglot.

 

Thanks

[larryllix]

Hi  Larryllix,

 

I do have a C wire.   I actually have two identical units with nest thermostats and they have run fine for several years, so I don't think there is a general configuration issue.

 

 

While looking for solutions, I found an ifttt applet that already does what I wanted.  It took like 2 minutes to set up to provide the alerting I needed.

 

I will still look into further integration with polyglot.

 

Thanks

OK. I just mention it because two of my sons have Nest stats and both went dead after a year or so without the "C" wire that Nest "doesn't need". Keeping the battery charged depends on the HVAC equipment not running too long with breaks in between runs. In our Canadian weather that can be a problem with extremely long A/C runs with the last 40 year trend of undersizing A/C size to control humidity.

[Tim Wilson]

I had the same issue on one of my Nest thermostats where I didn't have a common wire. (The builder only used a four-conductor wire to one of my thermostats for some reason.) It ran for a while just like Larry's son's experience and then started exhibiting the exact behavior the OP describes. It might be worth checking the voltage reported on the Nest to make sure it's within spec. Mine was too low which suggested that the battery couldn't supply enough voltage without the common wire. I ended up running a new wire to the location which took care of the problem.

[m_theredhead]

Hi All,

Thanks for all the inputs.

 

Ultimately, a new hard start kit fixed the issue of the second stage compressor coming on in the afternoons.

 

As I noted, I found a recipe for IFTTT that was supposed to alert me if the temperature went above a certain threshold, but it never worked.

[larryllix]

Hi All,

Thanks for all the inputs.

 

Ultimately, a new hard start kit fixed the issue of the second stage compressor coming on in the afternoons.

 

As I noted, I found a recipe for IFTTT that was supposed to alert me if the temperature went above a certain threshold, but it never worked.

Unfortunately as posted by others Nest will not give out their local API. It is rumoured there are hacks out there but that would take a third party CPU to run some hacking software to get parameters into your ISY. Cloud works most of the time, but relying on IFTT is probably the least secure you can get.