Air Conditioning compressor and Fan won't turn on reliably

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Old 07-26-13, 08:42 PM
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Air Conditioning compressor and Fan won't turn on reliably

A neighbor has been without the A/C system almost all summer. He hired some local HVAC guys to look at his BRYANT A/C system and they replaced a starting capacitor on the compressor that got the unit working temporarily for that day. They got lucky! The system appears to work intermittently one day and not the other. He came over to ask for help and I really couldn't say no since I have a little experience with odds and ends especially electrical things, I am not an HVAC or electrical expert but I enjoy tinkering with all things. I went and looked at his A/C system and initially discovered that his digital thermostat (honeywell) would blink when we selected a cooler temperature than his inside house temperature which was already 89 degrees. We selected 75 degrees, cool, and auto on the thermostat, one fan kicks in but not the compressor or the fan on top of the radiator looking unit (condenser?). We went to the roof and opened his unit and verified that the compressor is not turning on nor the fan on top. We checked the voltage into the compressor and it was there on all three connections 120vac. We also checked the low control voyage which is 24vac on the top of the contractor I believe. We went back downstairs and tried cycling the system off and on and it worked, both the compressor and the fan started right up and we went back upstairs to verify that it was. We went back downstairs and left it on for a few minutes and thought about this and were really confused, we wanted reliability so we turned it off and tried to turn it on after a few minutes and the system went back to the original none working condition. To try to make it short this happened 3 times on that day, we went upstairs and checked connections and discovered that the wires from the thermostat were spliced outside the A/C unit right on top of the roof and all the insulation was deteriorated from the heat of the roof. We shut off the power and re-did the wiring splice to keep the wiring from shorting each other, then tried it again and the blinking thermostat still kept acting strange. We decided to pull the thermostat and as we were taking the cover off we discovered that 2 wires were off, the yellow and a blue wire. I tired to rewire it exactly as the wires were wired on the thermostat and popped the 5 amp fuse upstairs on the control board. We replaced the fuse and then realized that since the existing wires were so short the person that wired it cut a piece of the blue wire and extended the yellow wire in the wall to reach the thermostat with duct tape and wired the blue piece to the yellow terminal. I figured it out that I did not need that blue wire after popping the fuse and have since replace the thermostat with a newer digital honeywell thermostat and wired the Y-Y, G-G, W-W, and R- RC (with a jumper to RH). After we replaced it it worked well for a few minutes until we wanted to make sure it was reliable and we turned it off then it wold not come on again. So now after checking all the wiring and everything we could think of we are out of ideas. Would the Ignition control board be a possibility? Any Ideas that I can try? I removed the Control board and checked all the components that are checkable with a multimeter and they appear to be okay, nothing burnt. I will be going to his house tomorrow and want to try something beside re-installing the control board. I was going to order parts on the board if I notice a bad relay, resistor, capacitor, or component to try to save him money because I looked up this board and the cheapest one was listed for $287 and as high as $900 from one company.
 
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Old 07-27-13, 04:19 AM
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Did you read the manual about a built-in 5 minute time delay between compressor cycling. This built-in time delay is to protect the compressor from short cycling which can ruin it because pressures in the ac system have not equalized if restarted too quickly. Unequalized pressures cause the unit to start very hard and it may not be able to start at all depending upon how quickly the compressor is cycled.
 
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Old 07-27-13, 05:14 AM
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Shortly after my Bryant A/C went off warranty (it's now 21 years old), I experienced intermittent operation. Sometimes the compressor would start, other times it wouldn't. I removed the outside panel and looked at the wiring diagram (I'm an electrical engineer). As Kevin mentioned, there is a time delay component that prevents the unit from turning on shortly after it turned off (~5min). It turns out the time delay relay was bad. I went to the A/C contractor that installed the unit to buy a replacement part and was told that it was very common for those to fail, and that an alternative to replacing it was to install a digital thermostat (which has the time delay function built into it). I installed a digital thermostat, bypassed the relay, and haven't had any more intermittent problems. Take a look at the wiring diagram and see if the unit has a time delay circuit. If it does, that's likely the culprit.

Be advised that there is a downside to bypassing the relay (if that's the problem with your neighbor's unit). If you have a momentary power outage, you could have a problem, as the thermostat doesn't know that the power went out (it's battery operated), thus it won't delay turning the compressor back on. Fortunately, where I live, momentary power outages are very rare, so it hasn't been a problem for me.
 
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Old 07-27-13, 06:18 AM
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I'd also pull the contactor out and make sure the contacts are clean and there's no dead bugs preventing it from pulling in all the way.
 
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Old 07-27-13, 06:45 AM
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BOB's point is true as to the downside at least that is only if you don't use a thermostat that can be hardwired instead. It is very unlikely that a package unit has a time delay in the unit though.
 
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Old 07-27-13, 12:56 PM
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aibarra

Thanks for your inputs and advice on this, I will be going over to the neighbors right now and re-install his ignition control board. I removed this to check a few questionable components and they appear to be working fine. I will look for that timer device that Bob suggested along with the contactor that tom advised me on as well. I used to have an old Rheem A/C system where I could manually depress the top of the contractor and see the compressor and fan start right up, now with his Bryant A/C system that contactor doesn't appear to work that same way unless it is stuck closed. I will follow up and let you guys know what I find, if I can't get any closer to making this work I will continue to seek your advice and try any ideas that are worth checking. Thanks!
 
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Old 07-27-13, 12:59 PM
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please reread post #2............................................................
 
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Old 08-10-13, 09:29 PM
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aibarra

Sorry, it took so long to respond I got so busy with other things. Anyway I removed the contactor as tomf63 suggested and it looked almost new from the outside. I could not see the inside of the contacts since they have a cover plate on this contractor, so I started to remove the little screws on the plate and it fell apart. The contactor contacts were fried, the little spring that allows it to retracts vaporized. I ordered a replacement, installed it and the system is now working fine. Thanks again for everyones inputs! My neighbor and his family are happy and very grateful.
 
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