Hello

The reason for my burned out compressor was "bad contactor". Its contact fused together and causing compressor keep running when the inside unit is off.

Thermo shutdown perhaps will shutdown the compressor, but since the relay contact still close, the compressor then will try to start again later until it shut down again by it thermostat.

Keep repeat this condition for couple hours (or minuits? ) will burn out the compressor.

My question: Why don't manufacture use "double poles" instead of "single pole" contactor. At least if one contact fused together then the compresor still can not operate since the other leg is open.

As an EE engineer, I think the single pole design is really bad for this case. What do you think??

The thermostat in the compressor is called a overload.

There are many types of contactor/starters available to the HVAC industry.

Usually a bean counter decides what goes into HVAC equiptment not the engineer as I am sure you are well aware that our economy is driven by the cheapest cost parts to maintain a profit in a low dollar market.

Years ago all contactors were two pole design and of very high quality. Now they are junk and made in China or a similar el-cheap-o vendor.

Right now Goodman manufacturing got a bad bunch of the cheap contactors and the service men are replacing them all the time. To bad you have to run a service call on a 1 week old unit.

The manufactures went from a two pole contactor to a single pole when they cheapened up the units. This way they did not have to install a compressor crank case heater. They use a single pole with a always made one side of the 220 to allow current to bleed through the compressor windings to take the place of the crank case heater. This saved big bucks when you do this on 100,000 units.

I have 3 central air units in my house because it is zoned. On my annual inspections/service I always check the contacts for pitting and burning. First sign I replace it. If the unit calls for a 30 amp contactor I replace it with a 40 or 50 amp unit. This way I know it will take the load imposed on the contactor.

I had a small 37 man HVAC corporation years ago. The business grew because we paid special attention to items like contactors/relays/capacitors/compressor terminals/motor lubrication ETC.
Our service punch list was a long one and took time to do but I had high quality customers who did not mind spending a little more money for a job well done. It must have worked because I retired when I was 48 and never looked back.

I now teach augratis at a local university. While I have never requested to be paid I have the satisfaction of knowing that the students (some of them are contractors who attend class for credit hours required for recertification of there license) will be shown the right way to do our trade and our customers correctly.

I try to learn something new every day.

Thank you very much for the explanation.

Yes, to save couple cents for a pair of contact causing the home owner like me thousands of dollar.

How many home owner know that the average life of a relay. I think at least the manufacture should put this information in the manual to tell the consumer to pay attention to the relay's contact.

Anyway, Thank you very much for your helps in last couple of day.

Best regards,

Langle1033