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.
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:
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.
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:
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:
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.