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A repairman recently found that the actuator and the high limit switches were not working when our 15+ Carrier gas furnace was only blowing cold air. There are separate thermostats for the downstairs and the upstairs.

I understand that he bypassed both of these controls until parts were ordered.This was on a Friday and left operating at full capacity like that until the new parts were installed the following Monday. Meantime, when he returned that Monday the coil on top of the unit had overheated and melted, as did a section of the ducting. My friend who lives downstairs said after the repair, when he got home from work, the CO alarm was going off.

Can these controls be bypassed and the unit allowed to operate for 3 days? I thought that this method of bypassing these controls should be for testing the unit on a temporary basis for testing, not left to have it operating at full capacity for this length of time. Could this have caused the further damage that was not present that Friday? Also, could any of these factors cause the CO alarm to be activated after the final repair? I was out of the state when all of this happened.

Please advise. Thanks.

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Yes, you can bypass the high limit switch for testing. It's as trivial to do as it sounds.

It's the acme of foolishness to run it like that for any length of time, though, and I think you already know that it could cause more damage. The high limit switch is there to protect against the type of heat damage you describe, along with fire. I'm amazed that metal melted without burning down your house. And yes, CO can build up due to a clogged heat exchanger, which is probably what tripped the limit switch to begin with.

I'd get a different repairman and suggest to this one that he's lucky you aren't suing him for criminal negligence or unintentional homicide. Chances are what he did was actually illegal.

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    100%. Just comments because I don't have anything really different to say: I once had a problem where the blower fan wasn't getting started, so heat would start and then trip limit and stop because very little air was flowing through the air handler. HVAC tech figured that out and he hardwired the fan on until he could come back with the right parts, but (I hope!) he didn't override any safety limit switches. That was perfectly safe because it was no worse than if I simply set my thermostat to have fan "On" instead of "Auto". I've seen other "fixes" from other people over the years and... Dec 18 '20 at 2:51
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    I have made the decision not to call certain people (who come highly recommended by others) because I have seen that the workarounds they do as a quick fix just aren't safe (though not quite as bad as this one). Safety first! Dec 18 '20 at 2:52
  • Totally agree with isherwood, what a hack job. He's lucky he didn't kill someone or burn the place down. + Dec 18 '20 at 12:05
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    If you are in a civilized locale, a call to the licensing board would be in order. Where such things exist, they are supposed to ensure that people who work on systems that can burn your house down or otherwise kill you demonstrate a degree of competence suitable for that sort of work. That appears to be lacking here.
    – Ecnerwal
    Dec 18 '20 at 15:30
  • I agree - call the local licensing board and get them out before you get repair work done. Let them see how incompetent this guy was and get his license pulled before he manages to burn down someone else's house. The next person will thank you!
    – FreeMan
    Dec 18 '20 at 15:46

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