How to Check the CTB During a Cooling Call

The CTB (central terminal board) is a board that is often replaced unnecessarily. A CTB is simply a junction board since there aren’t any logics or relays on the board to fail. Below we will cover the steps for checking the CTB:



1. Check for 24VAC on Y1 & common at the thermostat connection.

2. Check for 24VAC on the ECON plug pin 1 blue wire – this is an output to the ECON

3. Check for 24VAC on the ECON plug pin 2 gray wire – this is a return wire from ECON.

Note: if you don’t have 24VAC, you will need to check the ECON PLUG in filter section or wire.

4. Check for 24VAC on the CLO1/COMP1 Plug pin 4. If you read 24VAC here, this will indicate there isn’t an issue with the ECON Section.

5. Check for 24VAC on pin 6 of the CLO1 PLUG

Note: if you don’t read 24VAC here, you have a pressure switch open.

Follow the information provided and you will be able to determine the cause of a compressor malfunction or if a compressor is not starting during a cooling call.