My ST7100 is starting to have 'problems'. Works OK most of the time, but sometimes if you have just HW on or just CH on and then switch on the other function as well, it emits a loud and prolonged buzzing. Any idea what this might be? Some sort of relay issue - but why?
As the unit is circa-1990 (!) I decided to find a replacement. Honeywell suggest the ST9400C as a "functional replacement", but I would need to replace the backplate and change the wiring a bit. Not a problem in theory, except......
My system is wired as shown here:-
Note that the relays inside the ST7100 are electrically separate, any inter-connection between the contacts being done by external jumpers. However the wiring diagram in the ST9400C manual shows that the 'common' on both relays are connected together internally, so I can't replicate the current arrangements.
Honeywell seems to sell quite a few 7-day 2-channel controllers that all look very similar, but I can't find any manuals online for the others.
Can anyone suggest a suitable replacement controller that will work with my current set-up, or else some work-around to use one of the Honeywell controllers.
Thanks!
As the unit is circa-1990 (!) I decided to find a replacement. Honeywell suggest the ST9400C as a "functional replacement", but I would need to replace the backplate and change the wiring a bit. Not a problem in theory, except......
My system is wired as shown here:-
Note that the relays inside the ST7100 are electrically separate, any inter-connection between the contacts being done by external jumpers. However the wiring diagram in the ST9400C manual shows that the 'common' on both relays are connected together internally, so I can't replicate the current arrangements.
Honeywell seems to sell quite a few 7-day 2-channel controllers that all look very similar, but I can't find any manuals online for the others.
Can anyone suggest a suitable replacement controller that will work with my current set-up, or else some work-around to use one of the Honeywell controllers.
Thanks!