Secondary heat exchanger cleaning

jarpan

I have a Lennox surelight gas furnace circa 1998. I was having my primary limit switch triggered for the last 2 months. My limit switch needed to be replaced after being tested. My blower is clean and the filter is replaced. The vent is not blocked outside. Out of desperation I remove the blower and crawled into the compartment. Upon inspection the secondary heat exchanger is filthy but the primary heat exchanger is clear. Normally I would just clean it and be on my way however I cannot access the secondary heat exchanger via this compartment since the primary exchanger is blocking the access. I do have access to the top of the secondary heat exchanger via an aftermarket humidifier installed by the previous owner but not the dirty bottom. Before I rip apart this humidifier is there any way to remove the primary heat exchanger to access the secondary heat exchanger?

Tim McElwain

Is this a furnace with the blower on the bottom blowing up across the primary(and only) heat exchanger. To the best of my knowledge this unit does not have a secondary heat exchanger as it only has one heat exchanger. If you crawled in then just take a vacuum cleaner with you and crawl in and clean away also a long handled brush will help. I suggest a mask and goggles for safety purposes. Or you could call a pro and also have a combustion analysis done while they are servicing your unit. Ask if the do combustion testing if they say no then call someone who does.

jarpan

Thanks for your comment. Yes it is one with the blower on the bottom. I believe the secondary heat exchanger was added on by the previous owner of the home when they install the humidifier. None of the paperwork or user manuals that I have for my furnace mentions a secondary heat exchanger. I am positive this is the part that I'm looking at however. The width between the primary heat exchanger bars is not long enough for my vacuum cleaner hose. Like I said before I'm able to access the top of the exchanger via a humidifier that was added on.

jarpan

Top view of exchanger. This is located right above the primary heat exchanger.

Tim McElwain

At least get the vacuum to clean the bottom of the heat exchanger. Use a coat hanger opened up to stick up inside and loosen any thing that the vacuum can't reach. You have to be creative. I have no idea what the previous owner could have added that would classify as a secondary heat exchanger.
Seconday heat exchangers are only found on Modulating/Condensing furnaces yours is not one of those.

jarpan

Thanks Tim for the advice. I don't know what they were thinking either. Off to get some coat hangers.

jarpan

Ooops duh... it's an air conditioning coil... lol either way its blocked and I can't get to it to be cleaned. Palm to forehead

JUGHNE

Yep, sure looks like an AC "A" coil. There may be a removable panel on the coil box itself. Then with that off there may be a removable "A" shaped panel on the end of the coil that will let you get on the air inlet side.....this is aluminum fins on copper tubing....full of refrigerant pressure. NO sharp tools or coat hangers to be applied.

If you can get access to the air inlet side of the coil, there is a small coil brush (whisk broom) with the bristles no harsher than a toothbrush. That may get the worst off. Then when the AC is running and the coil working up a sweat, there is INSIDE coil cleaner, (spray can for evaporator coils). Get the coil wet with sweat and shut down, apply cleaner.....follow directions. If the coil does not sweat during cooling season you have more problems. If coil is that plugged it may freeze up.

If blower wheel individual vanes are clean the AC coil is usually not that dirty. This may have been the second furnace that this coil has been mounted and they did not bother to clean it before reinstall....."git er done"...!

This reinforces the importance of good clean filters(Not the $.89 specials). They have to fit so all the air going into the furnace passes thru the filters.

Or you could have HVAC company pump system down, remove and clean coil, silver solder coil back in while flowing nitrogen gas, pressure test to 300 PSI with nitrogen gas, triple evacuate system with vacuum pump, open valves, check operation, probably add gas. But when you ask them to do this most likely you will be told about the inefficiency of your entire system and it is time for a complete up-grade.....maybe it is. But the ROI on that upgrade is a long time out. Most of the time I advise people to keep using/repairing it unless the heat exchanger leaks or the AC compressor dies. (I'm pretty old school though)

PS: actually that is a double palm to the forehead .

Tim McElwain

DO NOT USE A COAT HANGER ON THAT "A" COIL FOR AC!!!