AC system won’t run and a bad capacitor




Last week I was called out to a customer’s home in Carlsbad that I’ve worked for several times before. This time his complaint was that the central air conditioning was not working. He and his wife both work so they left a key under the mat for me.
When I got there I turned on the a/c and set it lower than room temp.

Nothing.
Went to the outdoor condensing unit and I immediately heard a loud buzzing coming from it.
Ok then, the outdoor unit must be getting signal (24VAC) voltage, because it’s buzzing. so it looks like the problem is going to be in the 240 VAC outdoor unit.

I popped off the cover and looked around. Immediately my eye was caught by the capacitor. The top of it was all bowed out and creased on one side.

This was an easy one. A fast visual inspection revealed that the split capacitor was bad and was not allowing the compressor nor the condenser fan to start because neither start windings were being energized.

A new 40 / 5 uF, 440 VAC “split” capacitor was installed and the unit jumped to life. While there I put my guages on the system to see how this R-22 system was performing.
It was a 73 deg day. The high side was indicating about 180 psi producing a latent refrigerant temp around 94 degrees, causing an excellent thermal transfer difference (or delta) of 21 degrees.
The low side was pulling about 60 psi or 34 degrees latent, with a sensible temperature on the low side of the outdoor unit at about 42 degrees. A slightly wider superheat spread would have been nicer and I was able to reason that the system was very slightly overcharged. I decided to let it be and closed it all up.

It takes a while for the house to cool down but that’s what happens when builders install an undersized (cheaper) unit for the size of a house.

A tip for cooling the house when you have an undersized unit:
Cooling down a very warm house will take just about forever to cool down. Best way to cool things is to start the a/c before it gets hot- so there isn’t an enormous heat load to dissipate.

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