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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Earlier today my thermostat (Honeywell Vision pro 800 - I

Customer Question

Hi, earlier today my thermostat (Honeywell Vision pro 800 - I think) indicated the battery was low. I replaced the batteries and the screen lit up & appeared normal but the A/C did not come back on. The fan works but nothing happens when I switch to cool. I noticed that the thermostat said "wait" & this did not go away after several hours. I changed the 580 function code to 0, the wait message disappeared, and the A/C came on. However in this mode, the thermostat rapidly cycles the cool setting on and off. When I change the 580 function code back to 5, the a/c will remain on for a few minutes then switch back to wait and won't come back on even after waiting for approx. 30 min...Any suggestions?
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: The A/C seemed to be working fine before I changed the batteries so it seems like it could be related to the thermostat but I really don't know.
JA: Do you plan on doing the work yourself?
Customer: Only if its something easy. I'm really just trying to get an idea of where the problem might be & if there's an easy fix or if I need to call someone.
JA: Anything else we should know to help you best?
Customer: No.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, so far it sounds like a thermostat electronics failure, however without the full model number of the thermostat and some information how it is wired I can't be sure that it is not a *communicating model.. in which case the problem could be with printed circuit board mounted on the blower inside the furnace/air handler.

If you can tell me how many wires attach to the thermostat, what color they are, and what terminals the wires connect to, (IF if its A,B,C,D and not R, W, Y, G, and C types of numbers the problem could be in the printed circuit board mounted on the air handler blower.

The problem could also be poor contact between one of the pins on the thermostat that connect to the thermostat sub base screwed to the wall.

Expert:  Phil replied 1 year ago.

Tell me a lot about your technical skills sets and if you have a multi meter or not so that I can coach you most effectively.