Economizers –Revisited Part 4


In this fourth and final post on Economizers, I’ll try to go through troubleshooting the mod motor and the logic module.  In the last post, we went over the enthalpy sensors and discharge/mixed air sensors diagnostics.  Now we begin  with the “brains” of the economizer — the logic module.

The majority of troubleshooting can be accomplished with the use of a few jumpers.  By using these jumpers, certain “results” should occur. the following is a step by step procedure for checking out the mod motor and the logic module:

  • Disconnect power at TR & TR1. Remove the jumper across P & P1.
  •  Jumper TR to terminal 1 on the logic module
  •  Jumper T & T1
  •  Remove leads from outdoor sensor at SO and +. Leave the factory installed 620 ohm resistor across SR & +.
  • Apply 24 volts to TR & TR1 by energizing the blower circuit
  •  When power is applied, the L.E.D. should be OFF on the module and the dampers should be in the CLOSED position.
  •  Next, shut off power to the unit. Disconnect the 620 ohm resistor across SR & +. (This simulates “dual enthalpy” and “ties go to the outside sensor” so the economizer should now open.)
  •  When power is re-applied, the L.E.D. should be ON and the dampers should drive to the FULL OPEN position

Using this “cheat sheet” chart, you can see how to use jumpers and what the result should be when you jumper certain pairs and when you disconnect certain pairs.

Honeywell econ Cheat sheet

Here is Honeywell’s check out procedure..  You can see it is basically the same thing above only they have a 1.2K ohm resistor you can use to simulate enthalpy.  This is a very good way to so it also but you need the check out resistor:

honeywell Econ  service

One other thing to keep in mind — some economizers use the Honeywell logic module but now use a Belimo actuators.   If you find the dampers are opening when they should be closing or visa-versa, check the “switch” on the motor to assure you have it set for proper rotation.

belimo_af

If you follow a few basics, the troubleshooting is easy, Don’t overlook electrical connections.  Loose or corroded connections can cause all sorts of problems.  This is especially true in restaurant kitchen units.  Grease is an acid (fatty acid) and will corrode connections very quickly.  It can also act as an insulator and prevent circuits from working:

photo2photo1

Lastly —  the most important part of all of this.  You do not need to get out your linesman pliers and start cutting all sort of wires.  When the economizer is not functioning and you need to get the mechanical cooling on, all you need to do is follow the steps below:econ by-pass

Hope these posts have been beneficial.  Hopefully, after going over all these posts –economizers are no longer the most mis-understood, mis-diagnosed, and most often gutted controls systems in commercial equipment.

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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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9 Responses to Economizers –Revisited Part 4

  1. Robert H says:

    Thank you so much for this review on economizers! I have researched them in the past and found almost nothing on the web. One question I can’t seem to find the answer to is purely airflow related: With our 5 and 10 ton rooftop units, when the economizers activate, the front doors will blow open with seemingly all the airflow blowing through the door. It seems, because the return air at the unit is restricted, there is no place else for the extra air to go. Is something set wrong? Return air damper going closing too much? I even put a wall motorized damper in but have not gotten around to figuring out the economizer contacts on the unit to hook up for some sort of relay control. I want to use the economizer throughout the winter to recycle air for 15 min each day. This keeps our radon way down (big problem in this area of Colorado). But, again, it just seems to be just building a lot of pressure in the building, especially when the doors are closed. This can’t be good for the blowers. Any advice? Thanks again. –Robert

    • what you need is a barometric relief damper in the unit so when you are using 100% outside air, the building does not go into a positive pressure. The other possibility is to install a “power exhaust in the unit. Talk to your manufacturer’s rep about htese for your equipment.

  2. Gary says:

    EXCELLENT! Searched the internet for a couple days for information this good. Thanks for your effort!

  3. guitech2014 says:

    Thanks Mike for taking the time to share with us. This economizer information was very informative.
    Can you tell us with the RTUs out there without an economizer but say with a motorized damper for ventilation, and say they are commissioned with a two position actuator for a minimum OA and OFF…Are these types of setups typically controlled with some logic module or are they triggered by the stat? Have you seen anything like this?

    Thanks again.

    • Paul– motorized dampers and/or 2-position actuator do NOT have logic modules. Typically, anytime the fan is running, the actuator goes to the “set position” to provide the set amount of fresh air. Unlike a manual damper that is open all the time, since these are powered off the fan circuit, they only are open when the fan is running and close when the fan is off.
      Hope this helps.

  4. Dominic says:

    I am working on a York RTU with a W7212 controller that has been disabled . I tested everything according to your article and made adjustments and it is operational. The customer space has a large heat load and can’t keep up when economizing . I read to wire a 2 stage tstat to bring on mechanical cooling to help the economizer. This W7212 has no wires present at terminal 3 and 4 . Can I still wire a two stage cooling stat to the y2 logic circuit board ? And is mechanical cooling going to run with the economizer open? Until the discharge temp sensor falls below the 55 degrees then the economizer is going to close? Once y2 is satisfied then back to economize. Or will the economizer close as soon as a y2 call comes in? I was told by local york tech support to not wire in a two stage thermostat , it will not work. RTU is a DH048N06P2AAA2A .

    • your unit would not have wires at terminals 3 and 4. The Simplicity Board in the unit controls the mechanical cooling. YES — you should have a 2-stage stat. Y1 would come into the board and then out to the economizer terminal 1. If suitable for free cooling, it stops there. IOf above enthalpy or dry bulb set point, it come back to the board and energizes the compressor. When Y2 comes into the board, it would energize the compressor until it was satisfied. The discharge temperature sensor will control the economizer damper position in both mechanical and free cooling.

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