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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 5648
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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Inside unit comes on and only runs about 30 seconds and shuts

Customer Question

Inside unit comes on and only runs about 30 seconds and shuts off. Outside unit doesn't come on.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.
Hello,So far it sounds like a bad printed circuit board. Tell me a lot about your technical skills background so that I can coach you most appropriately on how to trouble shoot this. We can go from there.
Customer: replied 1 year ago.
Retired service plumber. No experience with ac
Expert:  Phil replied 1 year ago.
Thanks, ***** ***** are able to locate the printed circuit board, generally in the blower compartment, you can do this test on it. Use a hair drier toslowly and gently warm the card to 120F (warm to the touch butnot hot and not over 140F)... if you get any change in behavior thatmeans the card is bad... A micro crack hasopened in the printed circuit at a solder joint, or inside its CPU inthat case .... or a short circuit has developed as the cardexpanded when you heated it. Constantexpansion and contraction as these electronics heat and during theirduty cycles over the years is what wears these cards out. Itis also a good idea to replug all of the connections in the unit,that burnishes any oxidized terminal connections and will sometimessolve the problem, especially at the printed circuit card and in anysensor molex connectors. Do that with the power off to the unit ofcourse. Thesecards are also damaged by Electrical Spikes caused by power failuresand lightning. These high voltage spikes can literallyexplode the fine 'wire' connections inside the chip. There is also ashunt type device, often printed on to the card that allows a highvoltage spike to arc across to ground harmlessly, some of these canwear out after a few times and allow the high voltage spike into therest of the card and the CPU micro-circuits. The high end printedcircuit cards use a large capacitor like device, or several inparallel, to capture and release such surges, these do not wear out. We can go from there. If the card proves bad, you might be able to replace it yourself. .
Expert:  Phil replied 1 year ago.
Ooops, that had some run together words in it. Use a hair drier to slowly and gently warm the card to 120F (warm to the touch but not hot and not over 140F)... if you get any change in behavior that means the card is bad... A micro crack has opened in the printed circuit at a solder joint, or inside its CPU in that case .... or a short circuit has developed as the card expanded when you heated it. Constan texpansion and contraction as these electronics heat and during their duty cycles over the years is what wears these cards out. It is also a good idea to replug all of the connections in the unit,that burnishes any oxidized terminal connections and will sometime ssolve the problem, especially at the printed circuit card and in any sensor molex connectors. Do that with the power off to the unit of course. These cards are also damaged by Electrical Spikes caused by power failures and lightning. These high voltage spikes can literally explode the fine 'wire' connections inside the chip. There is also a shunt type device, often printed on to the card that allows a high voltage spike to arc across to ground harmlessly, some of these can wear out after a few times and allow the high voltage spike into therest of the card and the CPU micro-circuits. The high end printe dcircuit cards use a large capacitor like device, or several in parallel, to capture and release such surges, these do not wear out. ----------------------