I tried the flashlight and mirror tip and I was able to see light coming through the A-frame at several locations, so I guess it’s not clogged

Also, the return was never opened to unfiltered air.

I had a tech look at it and he said the computer indicates that it’s shutting down the heat on limit, which tells us that the plenum is overheating.

We took the bottom door off to allow more air flow and that seems to have alleviated the problem, so I’m moving forward with adding more returns.

Thanks.

Does your horizontal A-frame evaporator coil look similar to this Goodman model? Can you get to both sides of the A coils?

If your challenge is getting access to the other side of the horizontal coils, consider installing a duct access panel in the plenum in front the coil case. Lau Industries and Kees make duct access panels. These are insulated duct access doors with a gasket to seal against the plenum and metal tabs (similar to a duct starting collar) which grip the inside of the plenum to prevent blowouts. Easy to install in the rigid plenum ductboard.

Were the return air ducts open during the remodeling such that air bypassed the air filter? If not, the air filter should’ve caught the construction debris/dust. Check the air filter isn’t dirty and replace it if necessary. Have you opened the air handler to inspect the coils by shining a high intensity flashlight through the coils to a mirror on the other side to see if they’re clogged or dirty? If the coils are in fact that dirty, your blower motor could be clogged and blowing weakly. I wonder if the dirt/dust may have built up on your flame sensor and burners, too?

If the return ducts were never open to unfiltered air, then I tend to think the problem isn’t with dirty coils or blower motor. But you can use the foaming coil clean as it’s self rinsing. Just leave the system off for 15 mins so it can wick down to the condensate drain pan.

AC systems are relatively safe to work with because there’s no flame, heat and natural gas or fuel oil as with a furnace. Furnace problems should be looked at by a certified HVAC tech. Assuming the coils aren’t restricting the air flow, you could have a problem with the thermostat, flame sensor, blower motor or other furnace electronics. Heat cycling on & off every 7 mins (~8.5 times/hour) is not normal.

Please post back with what you find.

Thanks,
Bob

I’m in the middle of a basement remodel project. Since heating season began in NY, I’ve noticed that my furnace hits a temperature limit during normal operation – the heat cycles on for 5 minutes, then off for 2 minutes). This happens several times while blower keeps running. It also seems to take a lot longer to get the house up to temperature.

I have central air, and it was suggested to me that it’s likely that some of the destruction/construction debris has entered the system and clogged the coils.

I was going to use the foaming cleaner since I don’t have access to underneath the coils, but I didn’t know if it was appropriate to use that product during heating season, since the coils won’t self clean via condensation.

Also had another idea; would it be reasonable to use compressed air from the top of the coils and a vacuum connected to the condensation drain to clean the coils? My thought is that the compressed air would dislodge the “hair” and the vac would remove it.

I’d get a 2nd opinion because a detached sensing bulb is a red flag for improper installation. You may have a 5 year warranty on the compressor, so have everything thoroughly checked.

It should be a rare circumstance that a home HVAC system requires an immediate change over from heating to cooling. Such an abrupt change means there’s something wrong with the house insulation or envelope. I can see heating on a cold night and when the day warms up, turning on the AC; but that would require hours of gradual warming when no heating or cooling is needed and there’s no risk of thermal shock to the evaporator coils.

There are thermostats that will automatically switchover from heating to cooling modes (and vice versa), but those have a deadband of several degrees so the two cycles aren’t in conflict.

The question reminds of episode of the Muppet Show when Scooter put the Eskimos and Arabs in the same dressing room.
Later, Scooter yells down to Kermit: “I got trouble up here boss!”
Kermit: “What?”
Scooter: “The Arabs and Eskimos are sharing a dressing room.”
Kermit: “So?”
Scooter: “So the Arabs want it hotter and the Eskimos want to turn on the air conditioner.”
Kermit: “…Try to get them to compromise.”
Scooter: “Oh they have compromised! The Eskimos turned on the air conditioner and the Arabs set it on fire!”