Luxaire Model DDUC-048


Old 12-04-02, 03:32 PM
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Luxaire Model DDUC-048

I have a question about the Luxaire Model DDUC-048, 4-ton, natural gas heating and cooling unit. I am having problems with flame roll back which is causing the unit to shut the main gas valve via the high temp switch. I have replaced the main control valve, cross-over tube and orifice, and tubing. I have checked and cleaned the main burner tubes which I thought might have been blocked. Still have the roll back. This unit has a purge fan that is at the end of the burner tubes that also is the vent/exhaust for the tube bundle. When I removed the cover for this compartment, I found a pile of insulation which I thought might have been evidence of a mouse. I snaked and blew through each of the five burner tubes and found no restriction. What I did see was a type of thin band that appears to partially block or restrict the exhaust gases. This band is partially corroded and I am wondering if the purge/vent fan might be pulling excessive combustion air into the tube at the orifice end causing the rool back. I talked to the dealer I purchased the unit from (10 yrs ago) and he didn't seem to know about the strip that I am referring to. Any advice will be appreciated. Thanks!!
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Old 12-04-02, 05:25 PM
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In order to get specific details on your furnace you would have to talk to someone with intimate knowlege on that model.

The factory would know but they will not normally talk to the end user due to liability reasons.

The dealer would likely be the one.
It may be unreasonable to expect free advice from a dealer when he makes his living at what your asking for.
Old 12-04-02, 05:45 PM
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flame rollout

you have done your homework. be sure the flue is unobstructed, no bird nests, etc. this would restrict the flow, yet keep the pressure switch pulled in. also the heat exchanger could have a crack/hole, causing the blower to blow back into the exchanger. does this happen before the blower fan comes on ? you say the unit kicks off on "high temp" switch. is this the roll out, or the high limit, is it automatic reset or manual? piece you describe sounds like a brace, welded in to hold it all together. excessive combustion air would not cause roll back in your case, my 2 cents.

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