tempstar

Too bad your mechanic is a parts changer. Start looking outside. Pay attention to the defrost cycle. Bubba

probly just a bad thermostat...

Still, suggest have a tek reset the defrost jumper to the 60 minutes position and keep him on full time so he can sit there and replace the fuse every hour on the hour--hint if you supply enough beer also have him piss on the outdoors unit just prior the fuse replacement.

Shut the unit down after 1 hour 29 minutes, then turn it back on. Repeat.

Problem solved.

the tstat was replaced the control board in air handler

the unit was installed a year and half ago with no issues till now, a new defost control board and coil temp sensor was replaced, the reversing valve switches from heat to cool, I also believe it is something to do with the defrost cycle. the unit had a older t-stat replaced with a white rogers, replaced control board in air handler also just trying to figure out what is going on, checked all wiring continuity thought of a possible short, I guess the next thing would be is check the charge, could be low causing coil temp sensor not to make to let it go in defrost

Id be looking outside for a short in one of the low voltage wires. The ones down in the unit where they are touching the copper. L.P. swich, H.P. switch, sensor, RV solenoid, etc. Bubba

I would guess the RV solenoid because it only seems to happen at 90 minute intervals. It could be the RV coil gone, of a wire shorted to the RV solenoid coil.

Normally Id guess that but the OP said: "the reversing valve switches from heat to cool" If its shorted it wont switch. Ive been finding the wires from the LP and HP switch and even the sensor touch the coppper and the vibration of the unit rubs through the insulation. Bubba