Yusef and a client?

Yusef Adama(not real name) has been in the HVACR trades for 31 years, Residential, Commercial, Industrial and Refrigeration and currently runs a small operation out of Southern California.

Heating, Ventilation and Air Conditioning, HVAC – a silly acronym for the most valuable thing man has created to advance Civilization. What, Yusef? What about Computers? Medicine? Food storage?

NONE of those things would not be possible in their current form without HVAC, so let’s get started.

Behold Your God (of AC)


Way back when we used Fire, people began to notice if you gave Fire an easy place to vent smoke, it will go that way, Later we discovered Pressure Differential, and used it to our advantage. Today we use a variety of materials including PVC plastic to vent our Products of Combustion, and have developed standards of safety to insure said PoC don’t mix with our breathing air. 

Yup, a that is a furnace alright.

Gas ranges, old boiler systems and floor furnaces all give off some PoC, but the legal maximum is 9ppm so that’s O.K. However any forced air furnace is limited to 3ppm. 

Bad burning gas


Good burning gas

CO and You: CO is cumulative in the bloodstream – you start out with flu-like symptoms, then it gets worse…and if you don’t catch CO poisoning soon, you will die. If you have a good running gas furnace, it will produce NO CO, CO is created by incomplete combustion, Modern furnaces burn really clean, but even an old furnace with a clean burn, Will. Not. Produce. CO. If your CO detector does go off, I, personally, would do the following;

  1. Check for a clear vent,
  2. Run the unit and check with my million dollar meter for actual CO,
  3. Check the combustion air supply,
  4. Check for living air incursion,
  5. Look for cracked heat cells,
  6. Check and adjust burners,
  7. Check and adjust gas valve manifold pressure.

Combustion air and You: Furnaces need oxygen to burn clean (as does all fire) and a separate air supply is provided for just that purpose. Seen a screen or 2 in the furnace closet? That’s combustion air and it needs to stay clear of blockage – so don’t store things in there, not good.

 Heat Pumps and electric heat: This is the fun one; First, they aren’t really AC in reverse, they require a number of check valves, 2 different metering devices for the refrigerant and a bunch of other things that make them work. When it gets below about 25 degrees, they lose the capacity to draw heat from the surrounding air and begin to freeze, this where defrost comes in…

“Why is my heater blowing out freezing air?” Defrost occurs via sensors in the outdoor unit, and flips it into cooling mode. This results in switching valves around and thawing the outside coil, then it flips back to heat… so hang tight, it will come back. If you have electric heat installed, this will temper the cold air until defrost ends. Heat pumps are really only useful in a clime like California or maybe Arizona, cause once you get below 25 or so your running strip heat, which is extremely expensive.

Back to modern furnaces: The days of fires and rollouts are long gone. Off the top of my head, there are; the centrifugal switch, the pressure switch, 2 rollout switches, a high limit in the burner compartment, another on the blower, the igniter itself, and finally the flame sensor. If any ONE thing fails, the whole machine will shut down, and you must unplug and reset the system to check those faults, takes me about ten minutes, unless there are birds in the vent,etc. 

NOT a birdhouse

Bottom line, you are much safer than even 20 years ago.

Yusef what can I do to be safe and enjoy my comfortable warm/cool home? Filters, if you don’t know where they are, find them! Or ask me 🙂 usually located at the bottom of a furnace in a closet, in the ceiling as in a filter grille, turn off your system before changing, and no less than every 6 months for a forced air system, here’s why.


The filter is to keep the equipment clean, not your precious breathing air!

The indoor coil is capable of acquiring tons of dirt, blocking air flow for heating, and cooling and destroying equipment that demands airflow. It is expensive to clean up, and quite embarrassing for the homeowner. 

Did someone say “dirt”?

How it Works:

Forced-air furnaces, work like this;

1. Thermostat calls for heat,

2. Furnace calls for inducer motor (or vent motor if positive pressure)

3. Centrifugal switch closes to turn on motor,

4. Pressure switch closes,

5. Control circuit goes through all limit switches,

6. Igniter is energized, (could be a spark igniter or a hot surface igniter)

7. Gas valve opens for 7 seconds,

8. If flame is produced, flame sensor sends a signal to the control board,

9. After 90 second delay, blower comes on,

10. Once the thermostat is satisfied, the exact reverse happens – starting with the gas valve.


Heat pumps, electric heat:

1. Thermostat calls for heat,

2. Compressor fires off and reversing valve engages,

3. 2 sensors calculate ambient and coil temps every 15 minutes or so,

4. When it gets too cold and the outdoor coil begins to freeze…

5. Unit goes into cooling mode, defrosting outdoor coil, strip heat comes on,

6. Unit defrosted, goes into heating, strip heat turns off.

Yusef what can I do? I’m cold! Go to your breaker panel and rest the furnace breaker, or if a HP, both outdoor and indoor breakers. What we are trying to do is clear a programming fault in the circuit board, it does work sometimes and can save you oodles of cash, worth the small effort IMO.

If not, call an expert. the most expensive thing in your house is your HVAC… but it’s often the most neglected. It’s what keeps you comfy, and it will kill you if you don’t pay attention. I see dog hair clogged filters that look like a fur wall and ask my BMW driving customers, “would you do this to your car?”

“No? But you do this to your half a million dollar home.” (I despise those types)

Don’t be afraid, enjoy your comfort and don’t panic – but be aware, nothing is perfect, and CHANGE YOUR FILTERS!