HVAC Troubleshooting: Provider RTU Failure

Gary McCreadie is an HVAC tech, the creator of hvacknowitall.com and the HVAC Know It All Podcast 

It was a heat August day, myself and my co-worker had been digging into some PM work.  We discovered one of many Provider RTUs with out energy and the breaker tripped.  

I returned a few days later to unravel the thriller.  First step was to close down the RTU from the native disconnect and reset the principle breaker, after the reset, the breaker stayed on and did not journey.  This instructed me the issue did not lie in between the breaker and native disconnect, it was hidden within the bundle unit.  A visible inspection did not reveal something at first and not one of the most important hundreds had any floor faults. 

Earlier than making use of most important energy to the unit I eliminated the R wire from the management circuit, this may cease any operation of followers, compressors, and many others. and permit me to verify for energy within the main and secondary places with out something beginning up.  It’s possible you’ll crucify me for this however I did the bump, the contactor bump that’s.  However by doing so, it revealed one thing vital that lead me in the fitting route. 

This video consists of the troubleshooting steps taken to disclose the issue

Now, this arrange is certainly attention-grabbing with a main voltage of 575V for the compressors and 480V for the followers.  The problem of upper voltage, as seen within the video, might have in some unspecified time in the future broken the motors that had been being powered.  To rectify the problem, the transformer that suffered harm was changed.  

On this video, watch because the transformer is changed to rectify the problem

After the restore I regarded nearer into how Provider was producing the 480V utilizing the 480V/240V to 240V/120V transformers.  My reference level was on the 460V to 24V management transformer.  Previous to the restore, the first aspect of the transformer was receiving 347V (one leg of a 575V circuit) on one leg and 290V on the opposite, this generated a voltage of 560V throughout the transformer.  The 290V was fed from the transformer meeting within the condenser part.  After the restore, the 290V feed had been diminished to 245V, which translated to 489V throughout the first aspect of the transformer.  So primarily, they are producing the required 480V by offering one leg of the first voltage and one leg from the secondary aspect of the transformer meeting on the condenser part.  

Fascinating name to say the least, glad HVACing 

Gary McCreadie 

Comply with HVAC Know It All on Instagram, Fb, YouTube and LinkedIn and LISTEN to the HVAC Know It All Podcast

Save 8% on purchases at TruTech Instruments with code knowitall (excluding Fluke and Flir merchandise)