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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8768
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I am getting a system mailfuntion with several errors. Outside Sensor Error Coil Temp

Customer Question

I am getting a system mailfuntion with several errors.
Outside Sensor Error
Coil Temp Error
25-invalid model
33-limit fault
42-inducer fault
32-low pressure switch open
Submitted: 2 years ago.
Category: HVAC
Expert:  Phil replied 2 years ago.
Welcome! We keep going until you have all of the information you need.[b/]. Extensive training & coaching also available.
Multiple malfunction indications some not related tends to point to bad printed circuit card. 90%+ chance of that in this case, but not 100%
Tell me please if you have a multi meter and some skill using it... I can coach you from there accordingly. or if this sort of thing is not in your bag of tricks tell me which direction you are from the center of the nearest city and I will look for a well rated shop or two for you.
Customer: replied 2 years ago.
I have one, but need to find it. Which circuit board do I test?
Expert:  Phil replied 2 years ago.
You test the circuit board where the wires that come from the thermostat connect.
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.
Constant expansion 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 sometimes solve 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 the rest of the card and the CPU micro-circuits. The high end printed circuit cards use a large capacitor like device, or several in parallel, to capture and release such surges, these do not wear out.
Customer: replied 2 years ago.
I am trying to find my multi meter. I have noticed that if I power off the furnance the blower will kick on for 5 mins before it shuts off. I can also manually cycle power to the conditioner and it will run for a little while but the blower won't run at the same time.
Expert:  Phil replied 2 years ago.
Have you done the heat stress test I mentioned in my previous posts?
I suspect that a bad PCB might be the cause of our problems.
We can go from there. Please rate my work so far so that I can give you extended time on this question.
We are on the honor system here. Please remember to rate my service before you leave today. If you need anything else, just let me know. You can continue asking follow-up questions at no additional charge.