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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I sent a question a few minutes ago but after, I wondered if

Customer Question

I sent a question a few minutes ago but after, I wondered if I was supposed to register first so I just registered and here is a shorter version of the same question: I am writting on behalf of my sister.
On a year old Rheem AC condenser unit model number 13AJA36C01757, the unit failed to start the compressor although the fan was still turning. The original installer returned and added one of these Supco SPP6 hard start capacitors. That fixed the problem for 12 months. Now it's back. The installer says he won't come back and fix it again because the problem is the age of the electrical panel not the AC unit. He won't give any other explanation nor elaborate on what it is about the panel that could be causing it. The new AC unit is attached to the same source as the previous Rheem unit installed in 1998. We have a 30A double breaker and a 30A fused disconnect. Neither of which have tripped or blown. 2 questions: Could I restore the unit by getting another capacitor and how long should they last. And 2, if every other appliance in the house works and the previous AC unit worked for 18 years in the same spot, what mysterious things in the electrical service panel would cause the new AC to fail so soon. The same contractor offered to replace the service panel.....for $6000 more dollars. The installation was permitted by the City of Los Angeles.
I took readings on the wires feeding the unit and during the split second attempt to start the compressor I saw 88 amps and 237V AC under load.
Any thoughts?
Thank You
Submitted: 2 months ago.
Category: HVAC
Expert:  Phil replied 2 months ago.

Hello, thats good work on the load test, the fact that the voltage didn't drop points to a good panel, but I have not seen it, so it may be overloaded with other appliances that were not on at the time so you got a good test result.

Tell me the size of the main breaker at the top of the panel, and any brand names you can see, especially 'zinsco' or 'Federal' (those have gone out of business are deemed hazardous).

You could try replacing the hard start kit, they are not expensive, and if that fixes it you will be good for another few years hopefully, however at age 17 or 18 your heating and AC system is statistically at the end of its normal life span... worth fixing but only if its not major or costs over a few hundred dollars.

Let me know, we can go from there

Customer: replied 2 months ago.
OK, well a couple things I guess didn't come through clear. The unit in question is pretty much brand new, installed in April 2015 and failed the first time in August 2015, which is when the hart start kit was installed. I was making the point that this unit was installed directly to the same source that the previously existing unit had been hooked up since 1998.
As for the panel, yes is is the dreaded Zinsco and I am aware of their notorious status in the electrical world. It is a 12 space box with NO main breaker. It dates to 1954. I agree completely that it would be good practice as a home owner to upgrade that box but the contractor saw the box before he installed it and had no comment or warnings for my sister but as soon as something goes wrong it's the box that is the only possible problem. Of course this is a matter for small claims court and I won't argue it here. I just need to help her get back up and running in a manner that won't void her factory warranty. Just so you know my level of expertise, I have been an electrician for the Studios here for 35 years but I don't know anything about air conditioning. I think my sister was taken to the cleaners and I'm trying to get her out of it. She spent $6000 on that AC and now can't use it. Not right.
Expert:  Phil replied 2 months ago.

Thanks, ***** ***** will not start, while drawing 88 amps (thats locked rotor amps no doubt) and with 237 volts across line one and line 2. **while its drawing the 88 amps and reading 237 volts** then something is wrong with the unit or the compressor.

Possibly a bad compressor run capacitor, you can check the micro farad rating on the capacitor as compared to the rating stamped on it... these generally go bad and and fail entirely or they are good. however a few just loose some of their micro farad capacity. So check that.

If the run capacitor is good and the compressor still does not start and run then the compressor is mechanically seized... in this case however, after 55 years in the business I suspect that the voltage is actually dropping below 200 volts when attempting to start. That would be expected with such a small panel, and with the zinsco breakers.

Triple check all that and get back to me, we can go from there,

Expert:  Phil replied 2 months ago.

Regarding the fact that the previous unit had run for years on that panel, the compressor that is interesting but unfortunately does not prove anything since this new unit also ran for some time on that panel... there are power factor issues that could be happening, the phases should be 120 degrees apart as you know, you can measure that phase displacement, it is possible that one of the two lines serving the new AC unit is is overloaded and has phase shifted enough to cause a problem, especially given the smaller wire size used on those older panels from the pole to the meter.

I would try replacing the hard start kit as a next step.

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