Omnistat 2 and HVAC issues

[Anthony A.]

i am having an issue with my omnistat 2 thermostat and my furnace and AC. basically, in order for my AC to start and function, i need to wire the blue common from the omnistat 2 to the furnace board. once i do that, it starts the AC no problem. but in the winter, having it wired this way does not allow the furnace to turn on. i have no idea why, but the only way to get the furnace working is by disconnecting the blue common wire. once i do this, i get heat. does anyone have any idea why this is happening and what i can do to fix it? tech support does not know. i tried using the HAI thermostat power supply and heat works, but not the AC. it tries to start the AC as i can hear the AC motor clicking, but it doesn't seem to have the power to turn it on.

any help would be greatly appreciated. thanks.

 

[pete_c]

Years ago with the HAI Omnistat RC-80 I had many issues with the power "stealing" piece of it and my furnace motherboard. An additional piece that was causing issues was the HA to HAI panel talking to the thermostat (pegging the thermostat at 90 for no apparent reason). First piece initially was disconnecting the HA box from the HAI panel (eventually downgrading HA HAI plugin software). Very low WAF with this issue.

I have a friend whom has an HVAC company and we kind of went back and forth with the issues. He proved to me that it wasn't the furnace MB one day by removing the RC-80 and installing an old fashioned very manual Honeywell thermostat (the old circular type). I was actually to a point of monitoring the LED status lamps on the motherboard (blinks and whatever) and had left a VOM hooked up to watch voltages. Some of the testing also involved using jumpers on the furnace motherboard to manually do what the thermostat automatically did to validate the furnace motherboards functions. My HVAC friend questioned my "need" to automate my thermostat via a computer and convinced my wife that it was not necessary.

Initially had tried all of the "fixes" recommended by HAI (comm wire, thermostat power supply module isolation box (30A00-2), etc) and finally what fixed it was a separate transformer for the RC-80 with a relay isolation 29A00-1. Initially even that caused some issues. I think what had happened though was that the on and off and constantly making changes had changed some of the initial base settings on the thermostat. I eventually went to "readjusting" every default value manually (without connectivity to the HAI panel) on the thermostat and it worked.

So in summary I would kind of use the same approach that my HVAC friend did for helping me with my HVAC/RC80 problems.

1 - disconnect the Omnistat from the furnace motherboard
2 - validate function of the furnace motherboard voltages and whatever (if the MB goes out it may be more expensive than an Omnistat to purchase).
3 - connect a "manual" thermostat to see if it functions fine with the wiring and furnace motherboard.

This piece will validate function of your furnace motherboard / manual thermostat.

I would then try installing a 29A00-1 with its own transformer to see if that helps you. I've left mine in place from when I had my RC-80 so I don't really know if the new RC-1000 would have caused some issues with my furnace. The RC-1000 has been in place now about a year or so with no issues.

 

[Anthony A.]

Years ago with the HAI Omnistat RC-80 I had many issues with the power "stealing" piece of it and my furnace motherboard. An additional piece that was causing issues was the HA to HAI panel talking to the thermostat (pegging the thermostat at 90 for no apparent reason). First piece initially was disconnecting the HA box from the HAI panel (eventually downgrading HA HAI plugin software). Very low WAF with this issue.

I have a friend whom has an HVAC company and we kind of went back and forth with the issues. He proved to me that it wasn't the furnace MB one day by removing the RC-80 and installing an old fashioned very manual Honeywell thermostat (the old circular type). I was actually to a point of monitoring the LED status lamps on the motherboard (blinks and whatever) and had left a VOM hooked up to watch voltages. Some of the testing also involved using jumpers on the furnace motherboard to manually do what the thermostat automatically did to validate the furnace motherboards functions. My HVAC friend questioned my "need" to automate my thermostat via a computer and convinced my wife that it was not necessary.

Initially had tried all of the "fixes" recommended by HAI (comm wire, thermostat power supply module isolation box (30A00-2), etc) and finally what fixed it was a separate transformer for the RC-80 with a relay isolation 29A00-1. Initially even that caused some issues. I think what had happened though was that the on and off and constantly making changes had changed some of the initial base settings on the thermostat. I eventually went to "readjusting" every default value manually (without connectivity to the HAI panel) on the thermostat and it worked.

So in summary I would kind of use the same approach that my HVAC friend did for helping me with my HVAC/RC80 problems.

1 - disconnect the Omnistat from the furnace motherboard
2 - validate function of the furnace motherboard voltages and whatever (if the MB goes out it may be more expensive than an Omnistat to purchase).
3 - connect a "manual" thermostat to see if it functions fine with the wiring and furnace motherboard.

This piece will validate function of your furnace motherboard / manual thermostat.

I would then try installing a 29A00-1 with its own transformer to see if that helps you. I've left mine in place from when I had my RC-80 so I don't really know if the new RC-1000 would have caused some issues with my furnace. The RC-1000 has been in place now about a year or so with no issues.

thanks for that info pete. im shocked that this issue isn't more widespread. i haven't talked to my hvac installer yet as he mentioned even before installing my HAI system that if there's any issues, it is from the automation system. truth be told, i think hes totally right. i too did all of the things tech support suggested trying, measureing how how much voltage across the line, validating the furnace mobo and also plugging in a standard digital thermostat (which controls the HVAC perfectly). i know its the rc2000/OP2 thats causing the issue. since the power supply module doesn't work, i may give the isolation module a try as well.

 

[pete_c]

When all was done my HVAC guy told me to throw out the RC80. I did not and was determined to make it work and that's when I checked the default values of the thermostat.

BTW - some of the values had changed to numbers which didn't make any sense and were not even listed as standard numeric values on the RC-80 documentation which I believe compounded the problem. So regarding the "issue" for me it was both the power stealing issues and the communications between the OPII panel and my HAI plugin (thermostat) trying to compensate (with faulty logic?). The values though that I write about were the ones attached and the numeric values I saw didn't make any sense.

 

[morningla]

I think my problem was similar to yours.
tech support helped me through this back in 2005/6 and purchasing the 29A00-1 circuit board did fix my issue. (too bad they don't just ship an AC adapter with it so you have to also get this, like at homedepot).
HVAC people didn't really have any idea about automation at that time unless you paid them to come and troubleshoot this.

In my case, everytime the temp drops below my HEAT setpoint, the fan kicks in but the OMNISTAT will lose power for a short time and reset (this would have been ok if the OMNISTAT came with the option for a AA battery backup like most thermostat).
Watch your OMNISTAT too see if the power goes out when your furnance tries to ignite. (or AC in the summer).

This means, the furnance burner receives the signal to activate but gets cut off right after bc the OMNISTAT loses power and i guess the default is OFF for the furnance.

with the 29A00-1, it provided continuous power to the OMNISTAT while other functions are firing.
I am not sure what is causing the interface but that was the solution proivded by SmartHome at that time.
i don't think the 29A00-1 was too expensive. Good Luck.

Note, I have no AC on my HVAC so not sure if it's the exact issue.

 

[Anthony A.]

thanks for the help guys. i installed a thermostat power supply module (30A00-2), but it doesn't seem to do anything for me. My next step will be to try the isolation module as suggested. hopefully this will fix the issue, if not im gonna have my HVAC guy back and see if he has any ideas.

 

[pete_c]

Yes what fixed it for me was the 29A00-1 and an Elk transformer. BTW its starting to get cold and I noticed that I couldn't turn up the heat higher than 68F. After a few minutes of fiddling noticed the upper limit was set to 68F.