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Confirm diagnosis: Horizontal-left, 58MCA, collector box drain leak-->rollout

Confirm diagnosis: Horizontal-left, 58MCA, collector box drain leak-->rollout


Old 03-27-20, 01:42 PM
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Confirm diagnosis: Horizontal-left, 58MCA, collector box drain leak-->rollout

Have a horizontal, left-discharge Carrier 58MCA which tripped on flame rollout yesterday and I think I have the root cause identified, but would appreciate the expert opinion of someone like @PJmax (if I may be so bold as to ask a fellow north NJ resident for help). Symptoms as follows:
  • Code 13/33 registered yesterday morning and found to be a flame rollout switch trip
  • Reset and watched as it restarted and flames are blue and steady, but the top one has a small "tongue" of flame which isn't being pulled fully into the exchanger. The metal where that tongue impinges on the burner box obviously heated up, which I assume migrated back to the switch and was the cause of the initial trip. No real rollout or blow back witnessed.
  • Had noticed a bit of that telltale "secondary HTX issue" formaldehyde stink outside in the exhaust the past few weeks but was hoping to get through the busy COVID season at work before digging into this.
  • Inducer differential pressure switch hasn't tripped, but the exhaust almost sounds like its gargling some water with a bit of a surging sound. More on that below.
  • And here we come to what I think is the root cause...the collector box drain hose has developed a slight leak right where it is bent (see attachment), between collector and the condensate trap. That means the leak is on the negative pressure side of the inducer.
  • I watched until the end of the cycle and after the inducer shut down, built up condensate started leaking out of the crack where it hadn't been leaking with inducer on. That means the secondary HTX isn't draining. That condensate smells like the exhaust, and happens to drip through an access hole in the furnace exterior housing and that drains to a sump, so I hadn't noticed it without a closer look.
Based on the above, I believe the inducer is drawing air through the cracked tubing, into the collector box, back into the secondary HTX causing condensate to become entrained in the exhaust hence the smell and gargling/surging noise outside at exhaust. That crack is also allowing air to be drawn in downstream of the combustion chamber which would mean less air drawn in the combustion intake, which means less driving force for the flame into HTX and...there's the minor rollout issue.

Thoughts? Trying to forestall the inevitable secondary HTX failure of this cursed design.

Thanks in advance and sorry for the long read.
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Old 03-27-20, 02:24 PM
Join Date: Oct 2016
Posts: 1,720
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It’s likely the secondary.
The exhaust smell and hot burner box are usually the giveaway signs. I’d bet that a combustion test would show CO through the roof.
Id not suggest running it. Some of those have put so much CO out the exhaust that’s it’s leaked back into the house and sickened the occupants. 1000+ PPM of CO isn’t healthy to be anywhere near.....
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