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Is my HVAC high limit switch working or not? Two HVAC pros said it is.

5 years ago
last modified: 5 years ago


I have a 0.75HP Carrier HVAC unit, which works almost perfectly. One issue is that after running heat(but AC has no issues) for about 20min, it shuts down with only the blower motor running as if to take a break and to cool down. I can also see that it flashes code 33, which says that the HLS was tripped. I had 2 HVAC pros come take a look, and both left with nothing. One said that it was not getting enough air back, so I ran it with both doors open, so it can take as much air as it wanted, same happened. The second Pro observed the system for a bit and said that there is actually nothing wrong at all, and in fact I have a L180-20F HLS, which is doing its job by letting the unit cool down after hitting 180F. I asked him, but did not hear back of why does Carrier make a system that heats up to over 180F only to be shutdown by a safety mechanism? Seems like it should not be going up that high in the first place. However, I know nothing about this, so this is only my thought against that of a professional, so wanted to get some feedback here if possible. Can this be normal behavior? Thank you.

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