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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22542
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Attended service call for Carrier RTU Moel 48TJE008-511QE.

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Attended service call for Carrier RTU Moel 48TJE008-511QE. No Function Unit Dead Found 5 Amp Blown Fuse on Control Board replaced fuse unit Ran For few minutes & went out again.
You have a short in the low voltage circuit. If it ran for a while I suspect a contactor with a bad coil.
Customer: replied 8 years ago.
Billy thanks for reply & explanation. I re-visited service call today looked around in low voltage wiring did not notice anything but found wiring harness for economizer laying at bottom (in water puddle inside unit overflowing from drain pan) cleaned & dried wires pluged new fuse unit ran for good 5 hrs just recived call unit just stopped.
If that plug fell out once it may have done it again. Zip tie together.
Customer: replied 8 years ago.

Billy, Hello. I had it secured it properly also all 3 contactors, cond fan motor & both pressure switches were replaced prior to me visiting this call in last few months.. Is there any other tips i also picked up new control board which i wanted to change but was holding

I would check the contactor. The contactor could have a bad coil. The issue is not a direct short to ground or it would blow right away. If the unit has an economizer that is opening at night..there could be a short in that component. Start jotting down time of failures, conditions etc. and we will try to find a common denominator. IE- always at night, after 5 hr running, rain, etc.
Customer: replied 8 years ago.
Economizer is disconnected jumper plug is in place. This unit had lot of repairs done eg: both comporesssor replaced wires replaced for compressor terminals i will do what u have suggested since it is hour drive for me to call i will replace both contactors or any way to amp out coil volts.
I think it would be wise to replace the contactors. I bet you will find the problem rests there as long as all thermostat wire looks good. Let me know how it turns out.
Customer: replied 8 years ago.
Ok Billy thank u have great day.
You are welcome. Good luck.
Customer: replied 8 years ago.

Billy hello Again . Hope u had great day. I did figure out problem with ur help & tips./

Replaced all 3 contactors still it was blowing fuse after combing through wires blower fan relay gave clue traced wires n found wires from wiring harness going to economizer were exposed n touching blower housing i guess from vibration repaired wires unit is working one happy customer.



you are very welcome...nice find...those are the tough ones.
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