RC 2000 Brightness problem

[Anthony A.]

i, and HAI tech support, are stumped with my issue. i am hoping someone here has encountered this and can offer a solution.

my rc2000 was installed months ago and worked fine powering my furnace. when i installed the AC, it would click and try to start the AC motor but appeared to not have enough juice. turns out the common wire from the tstat was not connected back to the furnace. i attached the common wire to a piece of metal on the furnace (as per a suggestion to avoid using the power supply module), and VOILA! the AC now started up no problem.

for months, this setup has worked 100% perfectly. then suddenly, i go to the thermostat and the display lights up (because of the proximity sensor). but, there is no TEXT. to me, i thought the thing must have burned out so i ordered a new one. i put in the new one, set it up and it works perfectly for 10 mins. the next day, i go back to check up on it, and now the display lights up, but the text has faded about 50% of what it was last night when i installed it. so it appears something is burning the display characters.

tech support has me check the furnace power supply, thinking there may be a problem developing there and it isn't supplying enough voltage. i check it and it supplies a solid 27v, and 24-26v when the AC is running. HAI says to send in the thermostat for replacement, but this issue has happened on 2 different rc-2000's and i can't seem to figure out what the issue. why it worked perfect for months, then all of a sudden craps out? then 12 hours later, it does the same thing to a brand new one?

i was suggested to try adding the relay thermostat isolation module, but i don't see how that will help since i am getting the right amoutn of power from the furnace power supply.

any help/suggestions would be greatly appreciated.

thanks in advance.

 

[BrandonStapp]

the thermostat requires 24vAC, if you connected the thermostat "C" to the chassy of the furnace / blower, you are connecting it to a 120vAC GROUND ... I am suprised that it lasted that long. You need to go up there with a multimeter and find out where the transformer "COMMON" is and use that one!

 

[Anthony A.]

the thermostat requires 24vAC, if you connected the thermostat "C" to the chassy of the furnace / blower, you are connecting it to a 120vAC GROUND ... I am suprised that it lasted that long. You need to go up there with a multimeter and find out where the transformer "COMMON" is and use that one!

thanks for the response. i advised tech support of this and was told to pigtail 2 leads (from the thermostat) to measure the voltage while connected. they had me connect 1 wire to the C (common) and another to Rc (on the thermostat) and then measure how much power i was getting. i measured a solid 27volts. would i still get this reading even with using 120vac ground from the common?

 

[networkcrasher]

turns out the common wire from the tstat was not connected back to the furnace. i attached the common wire to a piece of metal on the furnace (as per a suggestion to avoid using the power supply module), and VOILA! the AC now started up no problem.

Brandon is referring to this line. It reads as if you connected the common wire from the t-stat to the chassis of the furnace. It should only be connected to the "C" terminal on the furnace. If you only attached this wire to the chassis of the furnace, it's effectively commonly grounded to the 120vAC ground. Not really a bit deal, but won't help the stat work.

On my RC-2000, I had the same problem. I had the correct wire attached to "C(ommon)" at the thermostat, but the stat would lock up and act weird. Once I realized it wasn't connected to anything at the furnace, I hooked that wire to the "C(ommon)" terminal on the furnace and it works perfect.

 

[Anthony A.]

turns out the common wire from the tstat was not connected back to the furnace. i attached the common wire to a piece of metal on the furnace (as per a suggestion to avoid using the power supply module), and VOILA! the AC now started up no problem.

Brandon is referring to this line. It reads as if you connected the common wire from the t-stat to the chassis of the furnace. It should only be connected to the "C" terminal on the furnace. If you only attached this wire to the chassis of the furnace, it's effectively commonly grounded to the 120vAC ground. Not really a bit deal, but won't help the stat work.

On my RC-2000, I had the same problem. I had the correct wire attached to "C(ommon)" at the thermostat, but the stat would lock up and act weird. Once I realized it wasn't connected to anything at the furnace, I hooked that wire to the "C(ommon)" terminal on the furnace and it works perfect.

got it thanks. i connected the thermostat common to the hvac common and also ordered a relay isolation module to keep the thermostat constant power with a separate transformer (just to be safe). what is the required power supply i need. is it a 24VAC, 5vA transformer and if so, can i get this from an electrical supply shop?

thanks.

 

[networkcrasher]

got it thanks. i connected the thermostat common to the hvac common and also ordered a relay isolation module to keep the thermostat constant power with a separate transformer (just to be safe). what is the required power supply i need. is it a 24VAC, 5vA transformer and if so, can i get this from an electrical supply shop?

thanks.

Honestly, I don't think you'll need the isolation module. Just try it with the common actually hooked up and see how it works. The manual for the isolation module should be online.

 

[Anthony A.]

got it thanks. i connected the thermostat common to the hvac common and also ordered a relay isolation module to keep the thermostat constant power with a separate transformer (just to be safe). what is the required power supply i need. is it a 24VAC, 5vA transformer and if so, can i get this from an electrical supply shop?

thanks.

Honestly, I don't think you'll need the isolation module. Just try it with the common actually hooked up and see how it works. The manual for the isolation module should be online.

well it appears that you guys are right. i hooked it up and sure enough its been 2 weeks now with perfect brightness. thanks for the tip.

on a side note, i now have an issue that stumps me (as well as HAI tech). so to recap, my hvac guy had initially installed the furnace and a digital thermostat without the common wire attached. when i got the omnistat, i simply hooked it up and all was well. once i added a conventional a/c unit, the onmistat didn't have enought juice to start it up. it tried, but couldn't. once the common was attached, it started up np problem. so the a/c has been working fine throughout the summer, but now that i call for heat i only get cold air. sure enough, i disconnect the common wire from the hvac and now i get heat. so it appears that i need the common attached for the a/c to work, but need to disconnect it for the heat. any ideas why and if a thermostat power supply module will fix this?