No communication with indoor unit fault

[ronnieray]

Bryant evolution 90i model 355AAV042060. Get a error message to contact technican. Dismissed notice and everything returned to normal. 36 hours later I get same message and again dismissed message the furance runs fine and the thermostat returns to normal look.

I went into the evolution thermostat diagnostics service menu and it showed a "No communication with indoor unit" fault had been logged. Also I checked the error code display on the furance and it has solid amber and green lights but neither are blinking an error code.

Any idea what could be causing this intermittent problem and lack of communication? FYI tfhe furance is 13 years old. TIA

 

[WorthFlorida]

Does your thermostat look like this? I'm familiar with these for Carrier AC units. If you do they are a proprietary unit and work on a 2 pair thermostat wire. One set is transmit data and the other a received data pair. Look at the controller board in the indoor unit. Where the thermostat wires terminated look for any wiring harnesses that may plug onto the card. There might be a small board about the size of a SD memory card with one or two resistors on it. Just unplug all harnesses and any modules and reset everything. There could be a intermittent connection.

The thermostat itself is two parts like most. A wall plate with connections then the top part. To remove the top part place a finger about the same position as the little flip door on each side and pull out and up just a little. It will pop off, then check the connections.

If it continues it's hard to say if it is the thermostat or the control board. These are extremely expensive thermostat and no longer made. New models are available and do not buy any that are used. I had eight of these for AC units and five of them had a defect in the program that seemed to show up after the 1 year when commercial warranty ran out. There are a lot of bad ones out there and they do seems to work OK until you have a power failure.

Since the controller board doesn’t show any alarms it could be the i/o port on the board or the thermostat.

 

[Sponsor]

 

[ronnieray]

Does your thermostat look like this? I'm familiar with these for Carrier AC units. If you do they are a proprietary unit and work on a 2 pair thermostat wire. One set is transmit data and the other a received data pair. Look at the controller board in the indoor unit. Where the thermostat wires terminated look for any wiring harnesses that may plug onto the card. There might be a small board about the size of a SD memory card with one or two resistors on it. Just unplug all harnesses and any modules and reset everything. There could be a intermittent connection.

The thermostat itself is two parts like most. A wall plate with connections then the top part. To remove the top part place a finger about the same position as the little flip door on each side and pull out and up just a little. It will pop off, then check the connections.

If it continues it's hard to say if it is the thermostat or the control board. These are extremely expensive thermostat and no longer made. New models are available and do not buy any that are used. I had eight of these for AC units and five of them had a defect in the program that seemed to show up after the 1 year when commercial warranty ran out. There are a lot of bad ones out there and they do seems to work OK until you have a power failure.

Since the controller board doesn’t show any alarms it could be the i/o port on the board or the thermostat.

Thanks for the reply. Yes that is the evolution control that we have.

It has been 2 days now and there has not been a repeat of the no communication fault. And both the thermostat and furnace have been working normally. I will however take your advice and check both the control board and thermostat as you suggest.

I have read elsewhere that sometimes the communication between the evolution thermostat and furnace can be interpreted by interference from other electronic devices in the home. Have you had any experience with this happeming? I don't suspect this is the cause of my problem since we don't have any new electronic devices and up to now things have worked fine, but I thought I would ask since it has been mentioned as a possible cause.

 

[WorthFlorida]

My only experience is with an AC unit. On boot up the air handler info and the outdoor compressor must match in size. That is determined by the plug In resistor board on the compressor control board. Without it nothing happens since the thermostat does not detect the compressor. I do not know if the furnace control board has one.

RFI is always possible but why after many years it would start! I doubt it. One thing with these proprietary thermostats, even with the new WIFI versions, BYW are really nice but nearly $500, once an error is detected a reset is always needed.

 

[ronnieray]

I noticed you mentioned the need to do a reset once an error is detected. How do you do the reset? Also, is it possible to clear the logged error codes on the evolution thermostat, and if so, how do you do it? Thanks again.

 

[WorthFlorida]

A reboot by turning power off at the furnace so the thermostat loses power or remove the thermostat from its base. After plugging it back together or restoring power you’ll see the thermostat display stepping through a start up process.

 

[ronnieray]

Thanks for the additional information and all of your help. Still no repeat of the no communications issue so I am keeping my fingers crossed. Cold already here is Minnesota and it's only going to get a lot colder. Last thing I need is a non functioning furnace at this time of year.

 

[WorthFlorida]

I stand corrected. The four wire thermostat wires are shown in this pdf file.

Each device in the Evolution System has a four-pin connector labeled ABCD.
It is recommended that the following color code be used when wiring each device:
A — Green = Data A
B — Yellow = Data B
C — White = 24VAC (Com)
D — Red = 24VAC (Hot)

http://dms.hvacpartners.com/docs/1009/public/07/pdsuid01.01.1.pdf

 

[KC27]

@WorthFlorida

I know it has been 1700 days since you posted your thermostat solution, but I just wanted to say thanks anyway. Several days ago, my Bryant Evolution central air was not working, with the thermostat displaying a "Indoor unit communications fault" - call technician message. I did as you suggested and separated the thermostat from the wall plate, sprayed the pins on the thermostat and the sockets on the wall plate with an electronic contact cleaner, reinstalled the thermostat on the wall plate, and that solved the problem.

The same thing happened a few years ago. That time I did call the technician. He told me not to worry about the message, that the system was fine, and that he had cleared the code. He probably just cleaned the contacts, too.

Thanks again

 

[KC27]

@WorthFlorida

I know it has been 1700 days since you posted your thermostat solution, but I just wanted to say thanks anyway. Several days ago, my Bryant Evolution central air was not working, with the thermostat displaying a "Indoor unit communications fault" - call technician message. I did as you suggested and separated the thermostat from the wall plate, sprayed the pins on the thermostat and the sockets on the wall plate with an electronic contact cleaner, reinstalled the thermostat on the wall plate, and that solved the problem.

The same thing happened a few years ago. That time I did call the technician. He told me not to worry about the message, that the system was fine, and that he had cleared the code. He probably just cleaned the contacts, too.

Thanks again

 

[Fitter30]

Also clean the ends copper wires and remake the connections.

 

[KC27]

Also clean the ends copper wires and remake the connections.

Thanks for the advice.