Economizers


Economizers are one of the most misunderstood, misdiagnosed, and most often “gutted” control systems on a HVAC unit.  Yet, when you understand them, they really are a simple control system.

There are 3 basic reasons for using economizers.

  1. They provide free cooling when the outdoor temperature is capable of cooling a space.  It costs less to bring in fresh air than to run a compressor — hence the name economizer
  2. They provide fresh air to the space to meet code requirements.  You can set the minimum position on the economizer to provide the code required fresh air.
  3. They now have capabilities to utilize IAQ (indoor air quality) sensors to control contaminants in the air in the space.

Basically, an economizer has 2 sensors, an outdoor enthalpy (temperature and humidity) or dry bulb (outdoor temperature only) and a discharge or mixed air sensor. Economizers only function when the indoor blower is energized (no sense trying to bring in fresh air if the blower isn’t running) and the “G” from the thermostat is what “powers” the logic module.

When a call for cooling comes in, the “Y1” is directed to the economizer logic module where it looks at the enthalpy sensor and decides if the outdoor air is suitable for cooling.  If it is, the economizer opens, bringing in the cool outside air and locking out the compressor.  Mechanical cooling can be brought on with a Y2 call from the thermostat if the economizer cannot keep the space cool enough.  If the outdoor air is not suitable for cooling, the logic module sends the Y1 call back to the main control and energizes the compressor.

A limiting sensor is provided to keep the air from being too cold going into the space.  That sensor is the discharge or mixed air  sensor.  It’s function is, whenever the unit is in “free cooling” with the economizer, the sensor maintains a discharge or mixed air temperature of 55 degrees.  It does this by modulating the return air and outdoor air dampers to blend the air to maintain the 55 degrees.

This is a very simple explanation of how economizers function. Trouble shooting, is really just as easy.  You need to check the enthalpy sensor and the discharge air sensor to make sure they are reading correctly.  You need to check for power at TR on the logic module (G from the thermostat come in here). You need to check to see if there is a call for cooling at the module terminal 1.  If you have a VOM meter, some jumpers, and a little patience, you can diagnose and repair any economizer out there.

I know this seem pretty simplistic, but, if you take your time; use your meters; you will find out how simple they really are to diagnose and repair.

Attached is a quick reference diagnostic  for troubleshooting economizers.  Hopefully, this will help you fix that control system instead of “gutting it”.

ST-014-07 Economizer Troubleshooting

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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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6 Responses to Economizers

  1. neil says:

    NEIL PATEL
    WE JUST HAD INSTALLED YORK 12.5T COOLING ANDHEATING SYSTEM AT MY BUSINESS WITH AREA OF 3700SQFT.
    SINCE THEY INSTALLED OUTSIDE WITH NEW DUCTWORK CONNECTIng TO OLD DUCTS.
    DO U THINK WE NEED ECONOMIZER AND IF YES WHAT KIND AND THERE MODEL NUMBER.
    UNIT WE BOUGHT IS YORK 12.5T 240VOLT
    MODEL # ZF150N15N2AAA5A
    SERIAL # N1E3752070.

    • Your best course of action would be to discuss this with your contractor. York does haver economizers that fit right into your unit. Your contractor would be your best source for determining the need, type, and application for your business.

  2. Isaac bright says:

    I am having problems with humidity. We have four zj060 units that cool 4-8 rooms each, this time of year when it rains and the humidity is high outside the economizer pulls the humid air into the rooms and we can have that because they process food products in the rooms that will get ruined in high humidity. Is there a way to shut off the economized function temporarily?

    • If the economizers have ENTHALPY controls on them, you could try setting the Enthalpy Set Point (dial marked A,B,C,D) all the way to D. That will only let the economizer open if the outdoor total heat is below 63 degrees and 50% humidity. If the unit is less than 7 years old, it has a Simplicity Lite board in it. On the board is a plug marked Econ, Y1, G, and occ. Remove the plug from the board and jump the pins marked Y1 and Y out. This will totally by pass the economizer and just allow mechanical cooling.

  3. Quinn says:

    Can you help me this problem on a carrier vvt, the problem is blower fan contactor is pulling, but a fan and the compressors contactor is not pulled,but I check a transformer is good, coil and contactor is new, do you think is a economise is bad? Thank you

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