Upstairs system thermostat showing code 53 ( temperature sensor error) and 89 (communication error). Inspected system, bypassed temperature sensor, checked wires and connections. Thermostat still showing errors. Called Carrier tech support for troubleshooting and thermostat and communication board need to be replaced. Possible other issues. System is low on Freon, capacitor is weak (according to last tech notes and pictures). System is 17 years old and some issues are happening. Due to the age and conditions of the system, Highly recommend to upgrade system, and bring warranty, comfort and efficiency back to the house. Main level system, is at same age , low on Freon and heat exchanger cracked. Best option would be to upgrade both systems, instead of spend lot of money on repairs. Set a lead to quote upgrades for the upstairs system, and possible main level as well, for tomorrow morning. Will get the price for new communication thermostat and call customer with repair price, but it ca