Carrier RTU 50 QD Series
I having problems with the primary side of the control transformer blowing after about a one minute delay
Main 60 amp line fuses are good. Checked and eliminated all possible and potential causes that I can see. Its 3 phase supply power, indoor fan motor is not single phasing equal amps and volts, compressors were ohmed and checked to ground, one or both of crankcase heaters was thought to have been the problem as I disconnected them during the troubleshooting and finally got the unit to run. I protected the primary side of the transformer with inline .5 amp fuses, however when I returned the fuses where blown again. I then changed the two contactors that are the pickup points for the power supply from the fuse block and once again the fuses blew.
This ones got me stumped. I meeting an electrician on site to help prove proper, stable main power
You are most likely experiencing an either constant or intermittant transformer secondary short/shorted load, wire, transformer winding,....etc.
You need to check your control circuit..not everything else. What's the transformer doing? What's it's loads?
What's the VA rating of your transformer? What's the primary and secondary current drawn?
I Agree! The problem is with the secondary! Measure amp draw on secondary. Check VA of transformer & divide sec. voltage = Max amp.s of secondary
Originally Posted by eastcreek
Problems with the secondary, (shorts, loads, connections) often burn out the primary because of gage of wire & inductive reactance.
Thanks to those who responded and yes indeed it was on the secondary side. After proving the line voltage was stable and correct and armed with a handfull of .5 amp fuses . We proceeded to eliminated components starting at the low voltage terminal board and defrost control board. Finally found one of the defrost temp control switches to ground.
With the low voltage fuse protection circiuit protection not opening that completely caught me and sent me off on the other direction.
Love this job and if it was easy everyone would be doing it
Next time you should hit up your local RadioShack for some .5 to 5 amp circuit breakers. I know that the ATC fuses are cheap but a little circuit breaker will last for years and is excellent for diagnosing problems like you had. Sometimes you can find them in a local supply house.
Originally Posted by JBocc
You have a bad outdoor air econimizer! Disconnect the wires at the plug and manually open for fresh air till the new one arrives!
"We stand on guard for thee" Canada