Proper Start-up – Basic Air Flow Set-up

Continuing with my series on “Back to Basics” and concentrating on why Proper Start-up Procedures are necessary to assure proper running equipment, the next thing we need to examine is setting up PROPER AIR FLOW for both residential and commercial equipment.

As I have been “preaching” in this whole series, too many contractors still think equipment is “plug & play”! What they feel is that the unit comes from the factory set for the proper CFM for the tonnage or heating capacity of the unit. What they do not realize is, again, the manufacturer sets the unit up for a “nominal” CFM but they do not know the application or job duct work or job static pressure.

On residential furnaces, a lot of manufacturers are shipping the heating speed of the fan on HIGH (this moves the cooling speed to a “medium” setting). They are doing this in “self-defense”  to keep units from tripping on limits. Now, the home owner complaint is the air feels too cold at the register. This is , at least, better that shortening the life of the furnace due to over heating” and usually causes the contractor to move the wires on the board to adjust the fan speed.  Hopefully when they do this, they take the time to properly set it up based on the TEMPERATURE RISE through the furnace. (see Heating Season — Temperature Rise post). 

Commercial units are probably the most “abused” when it comes to the idea of being set & run equipment.  The contractor feels, since he is replacing a unit with the “same size” unit, all he has to do is pipe and wire and leave. What he forgets is that someone had to set up the original unit to work properly on that application.  Now he has added a curb adapter, not even considering the added static pressure that causes, and never sets the CFM.

That alone is a problem, but, since most commercial units are belt drive blowers, was the belt tension ever checked? Was the pulley alignment ever checked to see if it moved in shipping? Are all the pulleys tight on their respective shafts? Is the drive pulley adjustment set screw tight?  So, does the contactor take the time to set his new unit up to meet the job specification for both heating and cooling CFM?

Now, add in the use of FREQ DRIVES to meet some of the latest standards in the industry, matching CFM to heating stages and cooling stages, and there is no way that unit is “plug & play” anymore.

It is coming down to the fact that INSTALLERS either need to be trained to perform the proper start-up or the contractor needs to figure in his quote having a qualified/trained SERVICE TECH perform the start-up. Think of it a new car dealer prep. We all know this is part of a car’s selling price and it should be part of any new piece of heating or cooling or packaged equipment.  Once we all realize this fact , then the necessity for proper start-up of any piece of equipment will become an integral part of any job.



About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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9 Responses to Proper Start-up – Basic Air Flow Set-up

  1. Larrry says:

    I went to a house today. The complaint is master bed room hot in the summer and cold in the winter. He had 3 contractors out to look at the problem. Two said to add a two ton unit for the master bedroom, bath and walkin closet. One recommended a zone system, with two zones. None did a simple TESP reading, 1.08″ wg. Over twice what the furnace could handle. I recommended a contractor that I understand knows how to check air flow. I too retired last year from JCI. The people that want to get better will read your blog, and improve their skills. The rest won’t.
    Keep them coming.

    • It still comes down to BASICS — Too many people are in too much of a hurry to do proper diagnostics. Most of the time, the problem is not the equipment but, rather, the installation — Thanks for your comment!

  2. Jim says:

    Then of course the final piece of the proper start-up would be combustion testing. If you start there then adjust gas pressure and look at the air flow after the gas has been adjusted for proper combustion you would have a proper start-up. I am not trying to break anybody’s stones but if you said charge an A/C unit to #325 head and #125 suction and don’t look at sub-cool or superheat it would be the same thing. To do a proper start-up you need to test and verify all three parts of a gas appliance Combustion, gas press (or re-orriface to get the proper combustion and gas pressure with in manufacture specs.) and Air flow/ Temp. rise. It would also be helpful if the manufactures gave us some combustion guide lines.

    • Jim — I couldn’t agree more but I am happy to just get them to do the BASICS. I do not know of a manufacturer that asks for combustion efficiency testing as part of the equipment start-up. That “fine tuning” is great and it can be a useful “sales tool” to tell the customer you are going to do this as part of the start-up which can ‘eliminate” the competition because they either don’t know how to do it or won’t invest in the analyze.
      Thank you for this comment — it is great to see there are people out there trying to do a complete and proper start-up.

  3. What ,when the Dealer All Temp Heating & AC in Waukonda IL refuses to do a Gasleak Check ,NOT nececery! Complaint to the officemanager- you did not smel gas, so it was not nececery. I informed him 11% Gas is explosion and i would not be 1in a Milion to tell about .I am a 27 year retired HVACR tech [S&C Electric Co.Chicago IL] Thank you Herb.

  4. Chip McClain says:

    I came upon this site not to long ago. Thank you for sharing your valuable info with everyone. Awesome site and i really appreciate all the work you put into it… Great job

  5. Robert says:

    Hey Mike. I have an air flow question. A system with the adjustable sheave that is closed will give a set RPM. Then as you open it the RPM changes by a few hundred RPM. How does this amount of change affect the unit. I have a unit as it is running on a single compressor does does not produce much condensation. Inside the building its 54 to 58%RH. I think due to the higher air volume the moisture doesn’t get to the condensate drain and dew point is not met. When I have both compressors running dew point is met in the evaporator an the unit produces lots of condensation. My question is should I open the sheave to slow down the air flow to get less air across the evaporator to take more condensation out. I think the air is moving too fast over the evaporator. Am I correct?

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