McQuay TGZ 040A

Questions and Answers:

K
Kenneth HickmanAug 20, 2025
What to do if McQuay TGZ 040A Water Heater has high discharge pressure?
- C
  Christopher JonesAug 20, 2025
  High discharge pressure in your McQuay Water Heater can stem from several issues: * Insufficient condenser water or water temperature being too high. Investigate ways to increase hot water supply or lower the temperature of the hot water and check the operation of the supplementary heater. * Fouled condenser tubes. Clean them. * Noncondensables in the system. Purge them. * The system might be overcharged with refrigerant. Remove the excess refrigerant. * The discharge shutoff valve could be partially closed. Open the valve fully. * The condenser may be undersized. Check the condenser rating tables against the operation.
A
amyalexanderAug 26, 2025
How to fix low suction pressure on McQuay Water Heater?
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  Collin MarshallAug 26, 2025
  Low suction pressure in your McQuay Water Heater can be caused by: * Lack of refrigerant. Check for leaks, repair, and add charge. * A dirty evaporator. Clean it chemically. * A clogged liquid line filter-drier. Replace the cartridge(s). * Clogged suction line or compressor suction gas strainers. Clean the strainers. * A malfunctioning expansion valve. Check and reset for proper superheat; replace if necessary. * Condensing temperature being too low. Check the means for regulating condensing temperature. * Insufficient water flow. Adjust the flow.
K
Kellie BryantAug 27, 2025
Why is McQuay TGZ 040A compressor noisy or vibrating?
- P
  perezstevenAug 28, 2025
  If the compressor in your McQuay Water Heater is noisy or vibrating, it could be due to: * Flooding of refrigerant into the crankcase. Check the superheat setting of the expansion valve. * Improper piping support on the suction or liquid line. Relocate, add, or remove hangers. * A worn compressor. Replace it.
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Alvin OsborneAug 30, 2025
What causes low discharge pressure in McQuay TGZ 040A?
- D
  Douglas CoffeyAug 31, 2025
  Low discharge pressure in your McQuay Water Heater may be due to: * A suction shutoff valve being partially closed. Open the valve. * Insufficient refrigerant in the system. Check for leaks, repair, and add charge. * Low suction pressure. See corrective steps for low suction pressure. * The compressor operating unloaded. See corrective steps for failure of the compressor to load. * The condenser being too large. Check the condenser rating table against the operation.
D
David HallSep 2, 2025
Why is the suction pressure high in my McQuay Water Heater?
- M
  Matthew CollinsSep 2, 2025
  High suction pressure in your McQuay Water Heater can result from: * Excessive load. Reduce the load or add additional equipment. * An expansion valve overfeeding. Check the remote bulb and regulate superheat. * Compressor unloaders being open. See corrective steps for failure of the compressor to load.
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Maria MorrisSep 7, 2025
Why does McQuay TGZ 040A compressor thermal switch open?
- C
  Cynthia BergSep 7, 2025
  The compressor thermal switch opening in your McQuay Water Heater can be due to: * Operating beyond design conditions. Add facilities so that conditions are within allowable limits. * The discharge valve being partially shut. Open the valve. * A blown valve plate gasket. Replace the gasket.
S
Sara HensonSep 9, 2025
What causes short compressor loading/unloading intervals in McQuay TGZ 040A?
- M
  Michael MitchellSep 10, 2025
  Short compressor loading/unloading intervals in your McQuay Water Heater can be caused by: * An erratic water thermostat. Replace it. * Insufficient water flow. Adjust the flow.
D
Dorothy SerranoSep 12, 2025
What causes the freeze protection to open on a McQuay TGZ 040A Water Heater?
- J
  James JonesSep 12, 2025
  If the freeze protection opens in your McQuay Water Heater, it could be due to: * The thermostat being set too low. Reset it to 42°F (6°C) or above. * Low water flow. Adjust the flow. * Low suction pressure. See “Low Suction Pressure.”
C
Christopher WilsonSep 14, 2025
What to do if McQuay TGZ 040A compressor will not unload or load up?
- C
  Carol MorganSep 15, 2025
  If the compressor in your McQuay Water Heater will not unload or load up, it could be due to: * A defective capacity control. Replace it. * A faulty thermostat stage or broken capillary tube. Replace it. * Stages not set for application. Reset the thermostat setting to fit the application.

McQuay TGZ 040A Specifications

General

Brand	McQuay
Model	TGZ 040A
Category	Water Heater
Language	English

Summary

TGZ Scroll Compressor Templifiers

Introduction

Overview of TGZ water heater units, their components, and design.

Water Pressure Drop

Information on water pressure drop through evaporator and condenser.

TGZ Electrical Data

Compressor Amp Draw

Table detailing compressor amp draw for various TGZ units and electrical configurations.

Field Wiring Diagram

Figure 4, Field Wiring Diagram

Diagram illustrating the field wiring connections for TGZ units.

Start-Up and Shutdown

Pre Start-up

Pre-startup checks and procedures before energizing the unit.

Start-up

Step-by-step procedure for starting the TGZ unit.

Weekend or Temporary Shutdown

Procedures for temporary shutdown and restart of the unit.

Sequence of Operation

Start-upCompressor Staging

Details on how compressors are staged on and off based on temperature.

MicroTech II Controller

General Description

Describes the MicroTech II controller's features and advantages.

Equipment Protection

Describes the unit's protection alarms and their functions.

Unit Mode Selection

How to select the operating mode (Cool, Heat, etc.).

Inputs and Outputs

Large PCO2 PCO3 Controller

Lists analog inputs for the PCO2/PCO3 controller.

Setpoints

Explanation of adjustable setpoints and their default values.

Events & Alarms

Protection (Shutdown) Alarms

Describes alarms that trigger rapid compressor shutdown.

Evaporator Flow Loss

Details the trigger, action, and reset for Evaporator Flow Loss alarm.

Condenser Flow Loss

Low Evaporator Pressure

Describes the low evaporator pressure alarm and freeze logic.

High Condenser Pressure

Sensor Faults

Describes faults related to various temperature and pressure sensors.

Limit Events

Low Evaporator Pressure - Hold

Event to inhibit staging additional compressors due to low pressure.

Low Evaporator Pressure - Unload

Event to unload compressors due to low evaporator pressure.

High Condenser Pressure - Unload

Failed Pumpdown

Alarm indicating pumpdown failure.

Controller Operations

Control Band

Explains the control band calculation for compressor staging.

Unit Enable

Unit Mode

Unit State

Evaporator Water Pump State Control

Evaporator Water Flow Loss

Logic for shutting down compressors on loss of evaporator flow.

Condenser Pump and Tower Control

Condenser Water Pump State Control

Defines condenser pump control logic for water-cooled units.

Condenser Water Flow Loss

Tower Fans (Cooling Mode Only)

Compressor StartStop Timing

Stage Up Now

Logic determining when a compressor stages up.

Stage Down Now

Logic determining when a compressor stages down.

Compressor Sequencing

Circuit Capacity Overrides

Low Evaporator Pressure

How low evaporator pressure affects compressor staging.

High Condenser Pressure - Unload Logic

Unit Capacity Overrides

Demand Limit

Limits unit capacity based on a 4-20 mA signal.

Manual Compressor Control

Normal Circuit Shutdown

Rapid Circuit Shutdown

EXV Control

Maximum EXV Operating Pressure

Prevents evaporator pressure from exceeding a set point.

Using the Controller

Navigating Through the Menus

How to navigate the controller's menu matrix.

Menu Screens

Menu Descriptions

Explains the content of each screen in the menu matrix.

View Unit Status (1)

View Unit Temperatures

View Circuit

VIEW CIRCUIT#1 (2)

Displays compressor status, hours, and starts for Circuit 1.

View Refrigerant

VIEW REFRG Cir 1 (1)

Displays evaporator and condenser pressures for Circuit 1.

View Tower

VIEW TOWER (1)

Shows tower fan stages and entering condenser temperature.

Screen Definitions - ALARM

Set Unit Setpoints

Set Compressor Setpoints

SET COMP SPS (1)

Setpoints for number of compressors and anti-recycle timers.

SET ALARM LIMITS

SET ALARM LMTS (1)

Limits for low evaporator pressure hold and unload.

SET ALARM LMTS (2)

Set Cooling Tower Control (TGZ in cooling mode)

TEST

Editing Review

Alarms

Security

BAS Interface

Protocols Supported

Lists supported BAS protocols (BACnet, LONworks, Modbus).

Optional Controls

Part Winding Start

How part winding start limits inrush current.

Hot Gas Bypass (Optional)

Allows operation at lower loads using discharge gas.

System Maintenance

General

General guidelines for periodic inspections and maintenance.

Operating Limits

Compressor Oil

Lists approved compressor oil types.

Sightglass and Moisture Indicator

System Service

Filter-Driers

Procedure for changing the filter-drier.

Troubleshooting Chart

Troubleshooting Chart, Continued

Continues the troubleshooting chart for various issues.

Table of Contents

Questions and Answers:

McQuay TGZ 040A Specifications

Summary

TGZ Scroll Compressor Templifiers

Introduction

Water Pressure Drop

TGZ Electrical Data

Compressor Amp Draw

Field Wiring Diagram

Figure 4, Field Wiring Diagram

Start-Up and Shutdown

Pre Start-up

Start-up

Weekend or Temporary Shutdown

Sequence of Operation

Start-upCompressor Staging

MicroTech II Controller

General Description

Equipment Protection

Unit Mode Selection

Inputs and Outputs

Large PCO2 PCO3 Controller

Setpoints

Events & Alarms

Protection (Shutdown) Alarms

Evaporator Flow Loss

Condenser Flow Loss

Low Evaporator Pressure

High Condenser Pressure

Sensor Faults

Limit Events

Low Evaporator Pressure - Hold

Low Evaporator Pressure - Unload

High Condenser Pressure - Unload

Failed Pumpdown

Controller Operations

Control Band

Unit Enable

Unit Mode

Unit State

Evaporator Water Pump State Control

Evaporator Water Flow Loss

Condenser Pump and Tower Control

Condenser Water Pump State Control

Condenser Water Flow Loss

Tower Fans (Cooling Mode Only)

Compressor StartStop Timing

Stage Up Now

Stage Down Now

Compressor Sequencing

Circuit Capacity Overrides

Low Evaporator Pressure

High Condenser Pressure - Unload Logic

Unit Capacity Overrides

Demand Limit

Manual Compressor Control

Normal Circuit Shutdown

Rapid Circuit Shutdown

EXV Control

Maximum EXV Operating Pressure

Using the Controller

Navigating Through the Menus

Menu Screens

Menu Descriptions

View Unit Status (1)

View Unit Temperatures

View Circuit

VIEW CIRCUIT#1 (2)

View Refrigerant

VIEW REFRG Cir 1 (1)

View Tower

VIEW TOWER (1)

Screen Definitions - ALARM

Set Unit Setpoints

Set Compressor Setpoints

SET COMP SPS (1)

SET ALARM LIMITS

SET ALARM LMTS (1)