HVAC overvoltage?

[kbsparky]

I had a customer call and complain that his house seems to eat outside A/C units on a regular basis.

Specifically, the compressors seem to burn out within a couple of years, where they should be lasting 15-20.

The HVAC guys are telling him that the power company must be supplying too little voltage, and that is what is burning them out.

So, I checked the incoming supply and measured 249.5 Volts. While that seems a bit high, it is within tolerance of 5% mandated by the PSC.

However, the nameplate on the unit states the rating is 230 Volts.

So, with an overvoltage of almost 20 Volts, that amounts to 8.5% too much, beyond an ideal 5%.

Would this be a factor, and should I recommend installing a buck transformer to lower the incoming voltage to closer to the nameplate rating?

The unit is a Coleman, self-contained heat/ac outside pak.

 

[Electric-Light]

What's the measured current vs name plate FLA?

Nominal voltages are 120, 240 and 480, but motors are always 115, 230, 460.

 

[kbsparky]

The nameplate stated minimum circuit ampacity to be 19, max breaker at 35.

I measured it running at 9.6 Amps.

 

[Electric-Light]

Are you sure its not losing refrigerant? The heat from compressor is rejected almost entirely through the condenser through refrigerant. If it doesn't have a low pressure cut out and it continues to run without refrigerant, I suppose it can burn out.

Sounds to me that HVAC guy is just looking for someone else to blame.

 

[Jraef]

Measuring voltage when everything is running is not the end-all answer. If the utility is routinely having brown-outs that could indeed damage the motors, but you wouldn't see anything until it failed or unless you happened to be measuring things right at that time. If he really thinks that is the issue or wants to prove it isn't, he'd have to have a recording meter connected to it for a long time.

There is a kind of "poor man's" version though. You could install an Under Voltage Relay that cuts power to the A/C compressor in a brown-out. If you also wired up a little cycle counter to a separate output of the UVR you could see how many times it engaged in a month, that could be telling. It wouldn't tell you what the brown-out voltage level was, other than being below the threshold of the UVR, but it would be good to see if, next time the A/C compressor fries, that the UVR didn't drop out even once. Takes away the "other guy" excuse from the A/C supplier.

 

[Electric-Light]

Measuring voltage when everything is running is not the end-all answer. If the utility is routinely having brown-outs

If that's the case, people would be complaining about flickering, lights being unusually dim, fluorescent lights having trouble starting and such. Remember, A/C condensing units are usually rated for use with 208-240v power source with +/- 5%, so in a residential distribution using 120/240 system and voltage drops to 208v -5% level, 120v would drop to 100v. It would make lights noticeably dim and people will complain.

Computers will continue to run fine since they're designed for 100-120 or in some cases 100-240, but the UPS will usually complain if power drops to 100v and it will give off beep.

If it's a PoCo issues, neighbors are going to be experiencing issues too. If it's a loose connection on that house, then lights will flicker big time every time the A/C kicks in to an extent that you can not miss it.

 

[kbsparky]

.... A/C condensing units are usually rated for use with 208-240v power source .....

I agree, however this particular unit does not have such a rating on its nameplate. 230 Volts is the only rating shown. Which is why I am asking about overvoltage being a factor more than undervoltage.

 

[Electric-Light]

Print this out and show it to the HVAC guy. Even if PG&E is not your PoCo, it's from a credible source and if he insists on arguing, have him call the local PoCo. Buck tranny is not necessary. If the voltage is out of whack enough to need such a thing, its the responsibility of PoCo to correct the matter, which in this case, it doesn't side it.

http://www.pge.com/includes/docs/pd...ergystatus/powerquality/voltage_tolerance.pdf

 

[kwired]

What is measured voltage at unit while running? Part of reason for many POCO supply services at around 250 volt is so that after voltage drop you hopefully end up someplace close to 240.

Does unit for what ever reason have to start frequently with pressure still in the refrigerant lines? Delay timers can be installed in control circuit, some units have them installed at factory. Brown out or malfunctioning controls could be the culprit of this. The brown out would probably be causing other problems that would annoy occupant and would hopefully be looked into.

Another thing is if the unit has had compressor burnout before has the lines been properly flushed of contaminants from the previous burnout? From what I understand, if not done properly the next unit will not last long.

 

[texie]

compressor failures

compressor failures

My bet would be on contamination in the refrigerant side due to all the pervious trashed compressors. It's so easy for the A/C guy to blame the power.

 

[Electric-Light]

Refrigerant turns into hydrofluoric acid which eats the insulation on coil. Put a new compressor, the remaining HF eats it again, it burns out.

I believe moisture in system accelerates refrigerant decomposition.

 

[Mgraw]

A simple acid test on the refrigerant would be the first thing the HVAC guy needs to do. If acid is present there are chemicals that can be injected into the system to neutralize the acid as well as filter dryers with "acid cores" that will remove the acid. Once acid is in the system it does not go away until it is removed or neutralized. If an acid test has been performed and there is no acid then I would look for power problems.