Honeywell RTH980 thermostat set-up

Hi All

I bought a couple of these units to install at home. First unit install went well, both heat and cold are working. Wiring was at both end as expected on old unit and Tstat, just had to switch the G wire to C at both end, put a jumper between Y and C on air handling unit and all was good

The second unit is giving me a lot more trouble. For the moment I have air handling unit working, heat (gas) working, but not the AC (or I can get AC working but not air handling unit)

The wiring on old thermostat and air handling unit was as follow:
G (thermostat) - Green (wire) to G (on unit)
RC - jumper to RH
RH - red to R (unit, via the sump level switch)
Y- blue (wire) to red wire (to AC unit) back as white (from AC) to blue wire to C (on unit) which from my readings it's how fan coil units are set-up (although I dont think mine is)
W- white to W (on unit)

Now I rewired it as per instructions:
G- empty
RC - jumper to R
R- Red to R (unit, via level switch)
Y- blue wire to red wire (to AC unit) back as white (from AC) to blue wire to Y (on unit) (kept it as it was, only moved it from C to Y on air handling unit terminal)
W- white to W (on unit)
C - Green (wire) to C (unit)
Jumper at air handling unit between Y and G

I tried to move blue wire in config above back to C (rather than Y on air handling unit) and then I had AC unit running but no air handling unit.

I have now put back all Tstat and rewired as orginally and all is working, I am baffled and running out of skills (not that I had any to start with! :D)

Thanks in advance for your help
Ludo

Honeywell RTH980 thermostat set-up