Testing a Furnace in summer

Is there any possible way I can damage the cooling system or unit when testing the furnace in the summer? The homeowner is blaming me that his unit is not cooling now. My test procedure for the HVAC system is to lower the A/C temp on thermostat cool enough to give the unit and house time to stabilize (usually as long as it takes to inspect the exterior), after inspecting the exteroir I come in, inspect the unit exterior and take my Delta T readings. When I am finished with that I take the cover off and inspect the interior of the furnace get unit info and see if gas is on, I then go to the thermostat and turn the heat on long enough for it to fire up and inspect the flame pattern, I then return unit to A/C mode. FYI the Delta T reading was a 3.5 before I turned on the furnace.

Start it up…Only after you cooled the place down in the cooling mode.

Not sure what your responding to Roy.

I am assuming that after you tested the furnace, and you set it back to AC, it was cooling?

Short answer is NO!

According to my delta t it wasn’t cooling properly before.

Since you made no adjustments to anything but the thermostat and a gas furnace has no deleterious effect on the a/c during prolonged heating operation and even less if it’s merely started up—otherwise it could not be installed in the same cabinet without harming the a/c—it sounds like you’re being set up. Please let us know what develops.


FYI, be careful about taking the heater cover off. Things will go wrong when you are in the attic, temperature is over 100 degrees and you cannot get the cover back on. TREC does not recommend removing the heater cover. Hope to see you at the convention this week in Bryan.

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I am wondering why you are taking Delta T readings? That is a diagnostic procedure. The SOP does not require you to determine the efficacy of the system. You could get into trouble when your extra effort conflicts with an HVAC professional who comes along after you.

All kind of problems exist in old house AC. Homeowners regularly cut registers into exposed ducts which then starve air further down the line. Additions which were never included in the original calculations have ducts added (oftentimes in poor locations). etc. etc.

Basic function the system comes on with the thermostat, blows cold air at each of the registers.

But if your qualified, and you like going out on a weak limb, knock yourself out!


Bob, when you inspect AC (assuming the ducts are intact, clean, blowing some air, the unit kicks in as it should) how do you determine if it needs further evaluation/repair from HVAC tech? do you not somehow assess its cooling ability? or do you always recommend repair/eval? do you not check to see if it’s merely circulating indoor air like a fan? wouldn’t that indicate an issue? wouldn’t that be so called determining “efficacy”?

Obviously the unit has to come on. There are plenty of hi, lo limit switches to prevent operation without adequate refrigerant charge. As I move through the home I check for temperature and air flow at each room register. Anything else is beyond the scope.

The SOP says:

IV. The inspector is not required to:
A. determine the uniformity, temperature, flow, balance, distribution, size, capacity, BTU, or
supply adequacy of the cooling system.

MD State SOP is similar.

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Can you expand on this, what do you mean? what temperature are you looking to see to “determine” if the unit is “functional” or not? or why are you checking the temperature?