Removed splices in thermostat wires and rerouted thermostat wire so it could go in the other side of furnace and not interfere with air filter replacement. Checked coil for air flow blockage. None found. Replaced thermostat with a 8444. It would not work in heat mode so installed a new s86w April air. Changed the furnace vent back to the original furnace vent. Customer said the the transition was getting so hot you could not touch it. Possibly restricted. Combination air is not hooked up need to make sure it is not restricted. System seem to be working good now.