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DuWayne, Master HVAC Technician
Category: HVAC
Satisfied Customers: 126
Experience:  Carrier Factory Trained. Service all Makes and Models. 17 years of experience
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I have a Honeywell PC8900 thermostat that no longer works and

Customer Question

I have a Honeywell PC8900 thermostat that no longer works and is discontinued with no cross reference on the Honeywell website. I bought a Honeywell RTH6400 thermostat as a replacement. The PC8900 wire terminals are labeled 1,2,3,4, but the RTH6400 are G, W, Y, R & RC. The current thermostat wire colors are wired to the following 8900 terminals:1-red, 2-white, 3-green, and 4-blue. The PC8900 is connected to a Honeywell Perfect Control system W8900A1004. On the upper left side of the system terminals list the 8900 terminals as is on the thermostat. The lower right terminals have the four colored wires on the following terminals: G-green, Y1-blue, W1-white and W2-red. I connected the RTH6400 as follows:G-green, W-white, Y-blue, and R-red. I left the jumper between R and RC terminals. The LED on the Perfect Control is flashing that it is operating properly, but the heat does not turn on. Any suggestions?
Submitted: 7 years ago.
Category: HVAC
Expert:  DuWayne replied 7 years ago.
ok so you left the jumper in correct?
Customer: replied 7 years ago.
Yes, I left the jumper between R and RC.
Expert:  DuWayne replied 7 years ago.
What is the equipment you are trying to run?
Customer: replied 7 years ago.
The furnace is an Amana GUVA045BX30, 46000BTU. I do not know the air conditioner brand or model. I can go out in the snow if needed. The perfect control system has a humidity and outside temp sensor installed. I also have an AprilAir 560 humidifier and a Honeywell Enviracare UV system installed on the cold air return.
Expert:  DuWayne replied 7 years ago.

ok i need to check the manual be right back

Customer: replied 7 years ago.
Is there another thermostat that would work with the PC system? If the RTH6400 does not utilize the humidity and outside sensors, can I bypass the PC system?
Expert:  DuWayne replied 7 years ago.
The honeywell Vision pro IAQ system is the new version of what you have and is exactly what would work here. If you dont have any other questions please hit accept or keep asking if you have more thank you
Expert:  DuWayne replied 7 years ago.

Here is the compatibility info for the stat you bought.....


5-1-1 Day Programming - Programming for the weekdays and weekend days
Energy Savings - Program to save up to 33% on annual heating and cooling costs (If used as directed. Savings may vary depending on geographic region and usage)
Easy to Use - Straighforward display and buttons keep operation and programming simple
Backlit Display - Easy to read, even in dimly lit rooms and hallways
Smart Response Technology - Continually adjust the pre-heating/cooling of your home so you are comfortable at your programmed times
Compatible - With heating and cooling plus some heat pumps
Does not work with heat pumps with back-up heat, multi-stage heating/cooling systems, and electric baseboard heat (120-240V)
1-Year Warranty


see the second to last about does not work with.

Customer: replied 7 years ago.
The visionpro 8110 has similar terminals as the RTH6400 I bought.
Terminal Designations: R, RC, C, W (O/B), Y, G, S1, S2

I will have the same issue of trying to figure out which of the 8900 terminals 1,2,3,4 match to R, RC, C, W (O/B), Y, G, S1, S2 of the new one. Any clues?
Expert:  DuWayne replied 7 years ago.
No im saying to replace the control module down by the unit as well it is called the Honeywell vision pro IAQ it will be the touch screen stat and the control module that goes down by the unit. These are 2 different systems the one you have is the old style The IAQ is the new version.
Customer: replied 7 years ago.
Thanks for your help, but I was able to figure out how to use the RTH6400 thermostat that I bought. The existing PC8900 system had humidity and outside temp sensors. My mother in law didn't need these functions, so I bypassed it and wired the new thermostat directly to the furnace.
Expert:  DuWayne replied 7 years ago.
Thank you for using my services if i can be of any more help just ask thank you.