Checking the Charge on a Heat Pump in the Winter

Checking the Charge on a Heat Pump in Winter

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Many people might say the best way to check the charge on a heat pump during cold weather is to "weigh in and weigh out" the refrigerant charge. While effective, this method may not always be practical for every situation.

If you are repairing a refrigerant circuit, weighing in and weighing out makes sense, particularly as microchannel condensers and scroll compressors make pumping down less viable. However, for routine checks to ensure the system is functioning correctly, this method might be overkill.

Originally written in 2003, these guidelines remain relevant for checking a heat pump's charge in heat mode.

Step-by-Step Guide

Step 1: Defrost the Unit

If there's any frost on the outside unit, make sure to defrost it completely before proceeding.

Step 2: Initial Checks

Examine the unit for obvious issues such as dirty filters, coils, and blower wheels. Ensure everything is clean for an accurate assessment.

Manufacturer Specifications

When charging in heat mode, always consult the manufacturer’s specifications first. For example, Lennox provides specific instructions that involve blocking off the condenser coil with cardboard or a charging jacket while running the system in cool mode to achieve the desired head pressure and subcooling levels.

In heat mode, remember that the evaporator is outside and the condenser is inside. A dirty air filter can cause low airflow and high head pressure, while a dirty outdoor coil can result in low suction pressure.

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Pressure Curves and Charts

Trane and Carrier provide pressure curve charts for their heat pump condensing units. Be sure to reference these charts when analyzing the system’s performance. Always follow manufacturer guidelines closely.

100° Over Ambient Rule of Thumb

The 100°-110° over ambient discharge rule is a widely accepted guideline indicating that a properly charged unit will have a discharge line temperature 100°-110° above the outdoor temperature. However, this rule should be used cautiously and not relied upon exclusively.

Old-School Rules of Thumb

Suction Pressure/EVAP DTD Rule

In an R22 system, suction pressure should be close to the outdoor temperature. For R-410A systems, the guideline is 20°-25° suction saturation below the outdoor ambient temperature.

Head Pressure/CTOA Rule

Typically, head pressure will be 30°-40° above the indoor dry bulb temperature, though this can vary depending on several factors like the unit’s SEER rating and indoor airflow setup.

Checking Without Gauges

When outdoor temperatures range from 65° to 15° and the coil is frost-free, you can perform a few quick checks without gauges:

• Discharge (vapor) line should be 100°-110° over the outdoor ambient temperature.
• Suction line temperature should be 5°-15° cooler than the outdoor temperature.
• Liquid line should be 3°-15° warmer than the indoor temperature.
• Indoor Delta T will vary with the outdoor temperature.

If any of these readings seem off, use gauges to verify—following manufacturer guidelines is always essential.

The best way to validate system capacity without gauges is by using dual in-duct thermometers paired with manufacturer specifications. This method can be challenging, so it might not always be your first step. We recommend checking out MeasureQuick for more precise readings.

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HVAC Preventive Maintenance

Just like a car requiring regular oil changes and tune-ups, your HVAC system needs periodic maintenance to run efficiently. The majority of HVAC system failures are due to dirt and rust! Preventative maintenance ensures reliable cooling and heating for your business.

Benefits of HVAC Preventive Maintenance Programs

These programs can save you up to 20% in utility costs. A study by ASHRAE found that a dirty central air system coil costs $600 more per cooling season than a properly maintained system. Adding a clogged filter can increase costs by another $480.

GTC’s Philosophy: The 70/30 Rule

According to GTC, 70% of HVAC maintenance should be preventive, while only 30% should be corrective. Regular inspections can prevent most issues before they cause significant problems.

Advantages of GTC’s HVAC Preventive Maintenance Program

Our detailed checklist includes changing filters, thorough cleanings, and inspections for leaks and wear, saving you time and reducing downtime costs.

Proper implementation ensures peak efficiency, saving on both maintenance and energy costs. Our program guarantees priority service during emergencies or disasters.

Contact GTC today to start saving energy, time, and money!