Old McQuay Chiller Control Panel – Electro-Mechanical ControlsOld McQuay Chiller Control Panel

This panel is part of the controls for an older McQuay chiller. New chillers whether they be McQuay, Trane, York, or Carrier chillers still require these types of controls in them to make them work. This part of this electro-mechanical control panel consists of contactors and switches (both manual and automatic) for electro-mechanical control of this chiller. To the right is the main power which feeds the unit with three phase main power. This power is first fed into a manual disconnect switch so that power can be secured to the unit if maintenance or repair is necessary. from there, the power is split between three separate loads. The first load the main power supplies is the compressors. Before the main three phase power arrives at the compressor contactors it goes through additional manual switches so the the compressor circuits can be isolated if necessary. The compressors have overload protection built into the compressors. The second load to which main three phase power serves is the fan contactors.

Old McQuay Chiller Control Panel

There are eight three phase fans for this chiller so there are eight separate contactors for each fan.The fans have overload protection built into them in the fan motors. The final load which is fed from main power is the step-down transformer. This transformer provides single phase voltage to other electro-mechanical controls (not pictured) which control the contactors shown in this picture. It is important that all the components in the chiller panel be checked for proper function along with all electrical connections being checked to make sure they are tight. Even older panels require special attention to make sure the electrical connections are tight and that the electrical components are functioning properly. Relays and contactors need to be checked for burned contacts that will stick and thereby fail to release when the contact is supposed to open. Burned contacts are the result of heat from arcing. When the contact closes sometimes there is a small arc of electricity across the contacts. The arc produces a tremendous amount of heat and the heat can cause the contact on the relay or contactor to melt or become softer. Over time this arcing of the electrical contacts can cause the premature failure of the contactor or relay.

Old McQuay Chiller Control Panel

The result is either a contactor or relay that sticks close or when it closes it passes the incorrect amount of voltage and current across the contacts which causes severe issues with electrical components including motors and other devices in the chiller system. For example, a motor that requires 277 volts will need plus or minus 10% of 277 volts to properly function. A 277 volt motor that receives 200 volts will over heat and possible fail. The failure can be catastrophic requiring the motor to be replaced. If the root cause of the failure of the motor is not solved when the new motor is installed then the new motor can also burn up as the old motor. Contactors can also chatter if they do not get the correct voltage. Some times the problem can be a relay that has burnt contacts which result in low voltage being supplied to the coil. Older contactors can chatter because the iron core of the contactor has rusted. Disassembling the contactor and sanding the iron core to remove the rust can take care of the contactor chattering. This control panel serves two large compressors, several solenoids, and several condenser fan motors that are staged on and off based on the temperature and pressure of the condenser. On cooler days with low demand only a few fans will run while on a hotter day with high demand all the fans will run to keep up with the demand. The chiller in the photo was a temporary chiller set up in a building under construction. The cooling tower for the new chilled water system in the building under construction was not scheduled for completion until the top floors of the building were completed since the cooling tower was to be installed on the roof. Since the new chilled water system would not be functional until the cooling tower was completed a temporary chiller was necessary to provide cooling so the drywall crews could begin installing the drywall. Installing drywall and then painting it in an unconditioned space will result in the drywall holding excess moisture and future problems resulting from the moisture. Finally, this type of control panel is from an older chiller. Modern chillers have microprocessor controls where precision control of the chiller adds efficiency and multiple levels of control. Many of the new chillers are able to be hooked up to a communication system that will talk to a building automation system. So the chiller can feed data to a computer control system and quite possibly the computer control system can make slight changes to the set points of the chiller.

High Performance HVAC

Old McQuay Chiller Control Panel – Electro-Mechanical Controls

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