Back in March, due to furnace blower issues and a service bulletin, the control board in my Carrier furnace was replaced & it worked great after that. Now I'm having cooling issues & I don't know if it's related.
So here's some background (sorry about the length):
58MVP100-F Nat gas furnace
38TXA048331 Condenser (1 speed)
Carrier zone control (2 Zones)
In Feb 06 we updated our Carrier system (installed April 04, Thermidistat thermostat) that included the Infinity 96 furnace, variable-speed blower, and 4 ton (I think) compressor (I think the comfort line as they’re NOT the 2 speed ones). When adding the new system 3+ years ago we made the older, existing system into an Infinity system (Infinitized them).
This “Infinitized” system has 2 zones (1 zone is the entire 3rd floor which almost NEVER calls for heat or cooling as we don’t use the 3rd floor, the other zone is 3 bedrooms & 2 baths on the 2nd floor, the stat’s in the master on the 2nd floor (ZONE1)) worked great last summer but now seems to have problems.
I noticed that the cooling seems to only come on at full blast until it reaches temp then shuts off. I also noticed that the dehumidify doesn't seem to work anymore. After noticing the strength of the system I went into setup thru the Infinity tstat and changed the Zone Airflow Limits to LOW on the 2nd floor zone (ZONE1, the one we use) & MAX on the 3rd floor zone (ZONE2, not really being used). This immediately slowed the airflow and seemed to work great.
Then a couple of nights later - I go to lower the temp & notice nothing is happening (I waited several minutes). So I go into the tstat settings and see the error (several times) "Airflow limited, Stagedown Occurred". I run it thru some tests & everything comes back OK. But the AC still won't come on. I then change the Airflow Limits to High on ZONE1, lower the temp again and on comes the AC but full blast (you can really hear it). If I change the Airflow Limit on ZONE1 to low WHILE the AC is ON, it will lower the fan speed and seems normal - but after it shuts off it won't come back on & I'll see the same Airflow error. The error only comes when the airflow is set to low on the Zone Limits. Also, as mentioned, the dehumidify seems not to work regardless of the airflow setting.
Any ideas? Could this be related to the replaced PCB in the furnace?