Carrier 178/179 fault

[Robbversion1]

At our home we've been having an on and off issue in regards to our Carrier fan coil and Bryant Multistage Heat pump. It seems like at random times throughout the year, the system would work fine until we start getting the dreaded 178 indoor/179 outdoor communication fault errors.

The wiring is setup with an ABCD setup with 2 data wires and 2 power wires.

Back in Nov 2018 we had a technician come out and replace the Fan Coil board, which I think fixed the issue at the time until it popped back up in Nov 2019. Since we have a hydronic/heat pump setup the heat would not turn on at all from either source. We found if we disconnected the yellow data wire going from the fan coil to the heat pump, the hydronic boiler system would finally take over and start heating. We left it like this for the entire winter not turning on the heat pump once. The spring rolled around and we decided we needed the heat pump to start cooling so we plugged the yellow wire back in. It worked fine for about a month until yesterday where we started getting the fault codes again.

We checked everything from the wiring to the thermostat, fan coil and even the Heat pump. The LEDs on the fan coil and Heat pump all show solid amber lights meaning they're in standby and even the comm light is solid meaning that there is some sort of communication.

Restarted everything a billion times this morning and couldnt get the cooling to kick in.

Now here's the kicker. I can get the system working again, but only if I have the system perform a checkout of the Heat pump - cooling. The heat pump and fan coil turn on and it does its little diagnostic test run. When I stop the test the system cools as it normally would. This is fine until the error pops up again (randomly from what I can tell). So this leads me to believe thats its not fully a communication error like the error code says since I can still control the heat pump with the thermostat.

At this point i'm at wits end trying to figure out what the issue is, so i'm posting here to see if anything has any idea of what is going on.

I know its alot of info that I put into this post, but honestly we spent upwards of $600 getting the system 'repaired' back in 2018 and would like some valuable input before we called in a professional again.

Thanks.

 

[WorthFlorida]

I’m assuming you have the high efficiency infinity model. Also you have the proprietary thermostat.

The original thermostat design were notoriously bad and were replaced with an all new design.

On the board in the outside compressor is a small plugged in card about the size of a memory scan disk. It only has two resistors on it and only two different part numbers. Depending on the size of BTU of the compressor determines which board to use. With the wrong size an error will display of a mismatch air handler and compressor. If if goes bad no communications.

Unplug this little board and clean the contacts, reinsert and give it a try. If you know how to use an ohm meter you can check the resistors.

 

[Sponsor]

 

[WorthFlorida]

This a the original bad thermostat. Don’t ever buy a use one like this. eBay sellers have no way to test them. I had eight of these at my church and five of them went bad after the warranty ran out. The new wifi replacements are around $500 each.

 

[Robbversion1]

Thanks for the reply. I actually have one of those newer Infinity Touch models. It's been pretty good so far. Nice to look at as well . As for the fault codes; the system has been running pretty good for the past 4 hours. When the fault codes come back (pretty sure they will), i'll go ahead and open up the heat pump and take a look at that card you mentioned. I'll keep you informed on how it goes.

 

[Robbversion1]

So I went and found that little board you had mentioned. Pulled it out cleaned the contacts as best I could. Also checked the 2 resistors and they appear to be within the tolerance range. Thermostat is still displaying the faults.

Noticed something last night. The thermostat has comfort profiles that activate at certain times (home, away, sleep, etc). If we do the checkout to force the heat pump to work, when the next comfort profile starts up we get the faults. So last night the heat pump was running fine until the sleep profile started at around 10pm then that fault came up.

 

[Fitter30]

Here a link for install manual look at bottom page 9 wiring
https://www.google.com/url?sa=t&sou...FjAJegQIAxAB&usg=AOvVaw0K6qdBUeHpaV6nmcAj2NZa

 

[Robbversion1]

So after countless hours of troubleshooting I think we were able to fix it. It actually appears the problem was with the wiring going out from the fan coil to the heat pump. Everything seemed to be ok when the heat pump was out of the equation. Since it was an 18/5 wire going out to the heat pump and only 2 of the wires were being utilized we just used 2 unused wires instead.

Its working like a champ now! I appreciate the help!