Editor’s Note: This article is excerpted, with permission, from the SK26-02 Service Training Package produced by Carrier Corp., Syracuse, NY. In this first segment, we address safety and the operational check.
Working on air conditioning, refrigeration, or heating systems means working on components that are pressurized, rotating, and either thermally or electrically HOT. So, be careful! Before performing mechanical service, shut off all the power ¯¯ open, lock, and tag all disconnects. Use extreme caution when troubleshooting electrically live components. Observe all safety procedures shown in printed instructions.
Don't take chances! Get extra help if heavy lifting is required. Some other advice to follow includes:
- Make sure all installation, modifications, and service work conforms to local and national codes.
- Wear safety glasses and gloves when working with refrigerants, power tools, and sheet metal.
- Remove watches and rings before performing electrical troubleshooting.
Following is a step-by-step process that should make you work fast, more efficiently, and do a better job of resolving chiller operation issues.
Typical Operational Check
The purpose of this check is to analyze the operation of a system so you can properly diagnose any problems. This should be done on a periodic basis, so that abnormal trends can be spotted early and serious problems avoided.
A typical operational check includes:
- A job site visit
- Observing equipment
- Comparing current operating data to both the design or initial data, and also to the preceding sets of data
- Correcting faults or malfunctions.
Before the jobsite visit, you should obtain the necessary service and maintenance literature for the installed chiller. Wiring diagrams are essential, and will normally be found on the inside of the control panel door. Contact your distributor for any necessary literature, and talk to your distributor’s service manager if you have any questions regarding the operational check.
Have the following tools available at the time of the visit:
- An accurate gauge manifold set
- Volt-ohm meter
- Clamp-on ammeter
- Digital temperature probe
- The correct refrigerant for the unit
- Standard hand tools
- Trouble light
In our sample operational check, we’re examining a water-cooled nominal 100-ton chiller on air conditioning duty. The chiller has a microprocessor control system. Many readings needed for troubleshooting are provided by a digital LCD.
Please note that not all chillers are equipped with this type of electronic display. If that is the case, the information must be obtained from thermometers and pressure gauges at critical locations in the chiller system.
A typical call to troubleshoot a chiller usually involves the chiller not being able to make capacity. The first thing to do is talk to the customer or operator and review the chiller's maintenance history.
Start by asking pertinent questions of what happened. Learn as much as possible, specifically:
- When and how the problem occurred
- At what point in the operation cycle the problem occured
- Under what conditions the problem occured
- What safety controls activated.
You also need to know whether there ever was a freeze up or any plugged tubes. Find out if there was ever a motor burnout or any other damage to the chiller.
Most chilled water systems are equipped with gauges and temperature measuring devices at critical points in the system. As the servicing contractor, it’s essential to maintain a log that includes the chilled water and condenser water temperatures, the condensing and evaporating saturated temperatures and pressures, and so on.
Figure 1 shows a typical recommended maintenance log. The maintenance log is a record of key readings and services performed on the unit. A space is provided to record the design temperatures and pressures so comparisons can be made. The maintenance log is a valuable tool, because by keeping careful watch on the log, you can detect developing problems before they become critical by comparing design conditions to actual operating conditions.
You should be able to find past log sheets, on the job site. If no log exists, start one.
When starting a new log, record the design conditions of the chiller. This design information should be available either at the job site or from the manufacturer's representative such as the local distributor's office.
If you can’t get design data, then use the data taken on the initial start-up of the chiller as a reference.
Record the actual operating system temperatures and pressures, for example:
- Chilled water in/out of the cooler
- Condenser water in and out of the condenser
- Chiller suction and discharge pressures and saturated temperatures
- Outside air temperature
- Actual suction line and liquid line temperatures for determining superheat and sub-cooling
- Amps and volts.
For chillers with two refrigerant circuits, take a set of data for each circuit. For simplicity, we will treat the chiller as a single circuit machine and will only use one set of data for our troubleshooting analysis.
After taking the readings, compare the current operating temperat-
ures and pressures with the design conditions and previous operating conditions to spot any trends that might be leading to trouble. Using the log sheets will help identify refrigerant side problems including:
- Air in the chiller
- Low refrigerant charge
Or water side problems including:
- Dirty or fouled tubes
- Low or high gpm, and
- Incorrect gauge readings.
Next month, we’ll discuss what measurements to take, how to record them on the log sheet and how to analyze the data once it has been gathered.