HVAC Diagnostic Chart: What You Need to Know

What Is an HVAC Diagnostic Chart?

Technicians use HVAC diagnostic charts to find and fix issues with heating or AC systems. Typical issues include things like heat pump charging problems, condenser faults, and dirty or blocked lines, 

As helpful as they are, HVAC diagnostic charts are a starting point. They don't give you the complete picture or tell you how to solve the problem. All they do is point you in the right direction, which saves time during the initial inspection.

For example, if you’re called out to a site where a heating system doesn’t heat the building properly, you’ll start by quickly checking system temperatures and pressures. Maybe they’re both lower than normal. Then, you can refer to the HVAC diagnostic chart, where you’ll find that an insufficient load might be the problem.

To get a clearer picture, you’ll need to do additional diagnostics, such as measuring the amp draw, to confirm and address the issue.

How Do HVAC Diagnostic Charts Work?

An HVAC diagnostic chart pinpoints problems without needing to dismantle the heating or air conditioning system.

Here’s how they work. Imagine you’re an HVAC technician or engineer called to the site to fix an HVAC system that’s been acting up. You head out with your tools. Upon arrival, you first open the diagnostic chart, which lists common issues, such as insufficient cooling. 

The columns show you what measurements to check, such as suction pressure, superheat, and subcooling. 

If you arrive at the site and the customer complains that their air conditioner isn’t cooling anymore, you can check the chart under ‘Insufficient Cooling’ and see that it tells you to look at low suction pressure or high superheat as possible causes. 

When to use an HVAC diagnostic chart?

In general, HVAC diagnostic charts are helpful in three situations—performing quick system checks, setting the charge, and conducting in-depth HVAC troubleshooting system faults.

Quick checks

Quick checks are usually done after a tune-up or repair. You don’t have to take anything apart; it simply means giving the system a quick once-over and taking a few readings to make sure everything works okay. For example, a quick inspection of the wet-bulb and dry-bulb temperatures will let you know if anything is off with the system humidity.

Setting the charge

If you’ve replaced a component within the system, you’ll have to reset the charge. This is an important step, as under or overcharging the system can cause problems. You should also check the airflow first, following the golden rule of ABC—Air Before Charging.

Use your diagnostic chart to check for problems caused by undercharging or overcharging. 

Troubleshooting

For complex HVAC issues, you can use the diagnostic chart to troubleshoot. Get all your tools ready and take measurements with gauges, psychrometers, and electrical meters. Compare your readings to the diagnostic chart to see if there is any superheating, subcooling, or other problem.

What Are the Main Components of an HVAC System?

HVAC systems move fresh air around a building, heating or cooling it, depending on needs. The main elements of an HVAC system are as follows:

• Compressor: The compressor pumps refrigerant around the system. When compressed, the refrigerant cools the air by increasing its own temperature and pressure. It is then sent to the condenser.

• Condenser: The condenser is where hot, high-pressure refrigerant vapors are cooled and condensed into a liquid on special coils. It is usually positioned outside the property, often on or near the roof. It is a big metal unit with one or more fans blowing out hot air when the AC is running. 

• Evaporator: An evaporator is the opposite of a condenser and is usually found inside your air handler or furnace. Warm air is blown over the evaporator coils. The evaporator coils contain the refrigerant, which cools down the air by absorbing heat and then evaporating.

• Air Handler: The air handler has a blower fan that circulates fresh air through the ducts after it has been cooled or heated.

• Thermostat: The thermostat tells the HVAC system when to turn itself on and off, maintaining the set temperature. 

• Ductwork: A system of pipes and tunnels that carry conditioned air from the air handler to various parts of the building and back again. You need well-designed and fully sealed ductwork to make your HVAC system efficient.

• Air Filters: These trap airborne particles such as dust and pollen as air moves through the system. All air filters must be kept clear to ensure good fresh air quality and maintain the HVAC system's efficiency. The air filter drier must also be in good working order, as it helps to remove moisture. If it’s faulty, you might have moisture-related damage and debris blockages.

What Are the Most Common HVAC System Issues?

Electrical issues

Electrical issues are usually caused by problems such as burned-out circuit boards, defective wiring, or a malfunctioning thermostat. These issues can lead to system failure or intermittent performance problems. Only skilled and qualified technicians should attempt HVAC electrical repairs.

Refrigerant leaks 

Refrigerant leaks compromise your HVAC’s efficiency or cooling capacity. Typical signs of this are higher-than-usual energy bills or poor temperature control. Sometimes, you might even see ice forming on the coils. In addition to leaks, it could be that your TXV (Thermostatic Expansion Valve) isn’t working properly.

Airflow problems 

If the AC feels like it’s not pushing out enough air, something might be blocking the flow. Filters could be clogged with dirt. Sometimes, the ductwork itself is to blame, being too leaky or poorly designed. This means all the cool air gets lost before it reaches you.

Superheat and subcool readings

Superheat refers to the amount of heat added to refrigerant vapor after it has evaporated from the evaporator coils. It is measured as the difference between the vapor and saturation temperatures. 

Subcooling is the amount by which the refrigerant’s temperature is below the saturation temperature after it has condensed. The high side (also known as the condenser side or the discharge side) is the part of the AC system where the refrigerant pressure is highest, so it must be kept within design specifications to ensure efficient operator and safety.

Heat exchanger faults

Heat exchanger faults can cause severe problems and damage, including dangerous issues like carbon monoxide leaks in the furnace. 

What Are the Limitations of Using Only HVAC Diagnostic Charts?

While great for initial troubleshooting, HVAC diagnostic charts are limited for more advanced diagnosis. 

One disadvantage is that they don’t account for different system specs, i.e., model differences, component variety, installation specifics, maintenance history, and climate. When you follow an HVAC diagnostic chart, you only get a small snapshot, not the whole picture.

As HVAC technology gets more sophisticated, diagnostic charts become less valuable unless regularly updated. Ever-changing factors like building design standards also impact the diagnosis of HVAC problems. To ensure you’re using up-to-date diagnostic charts, you need a centralized document system that stores everything in the cloud. 

How ServiceTitan Helps You With HVAC Diagnostics in the Field

The Field Service App for streamlined diagnostics

ServiceTitan’s Field Service App equips field technicians with direct access to property information, service history, and diagnostic data through a mobile interface.

You can input data and info into the app as you work, which updates system records instantly. Then, if another HVAC engineer comes along after you or you return for a follow-up, all the history is right there.

It means you’re always prepared with the full context of a property’s HVAC system.

Accurate job scheduling with ServiceTitan’s Dispatch and Scheduling features

ServiceTitan's Dispatch and Scheduling features help you assign the right technician with skills matching the job. The right tech on the job reduces the risk of misdiagnosis, incomplete work, and the need for follow-ups. This means you save time and avoid frustrating your customers.

The scheduling tool has handy built-in tracking features, which means you can see the nearest tech who’s a good fit for the job and direct them to the correct location. It’s the perfect tool for urgent calls and rapid response.

Streamlining call booking with property data for more efficient service calls

ServiceTitan’s Call Booking tool helps your office staff handle calls and scheduling more efficiently. When a customer calls, the tool pulls up info on the property’s HVAC system, such as service history, warranty details, how old the equipment is, and more. 

For example, if a customer has a recurring issue documented in their service history, the CSR can schedule a skilled technician. If they see the equipment is aging and out of warranty, they might suggest a maintenance check-up or discuss options for upgrading, saving the customer hassle later on.

Giving techs all this info before they arrive on site means they will be prepared with the right tools and parts. They’ll know what issues cropped up in the past and may even have an idea of what’s causing the current problem by matching the data with typical symptoms and fixes found in HVAC diagnostic charts.

Increasing revenue with ServiceTitan’s Pricebook and mobile app selling tools

ServiceTitan’s Pricebook and mobile app selling tools arm your field technicians with the latest pricing information, helping to boost sales and revenue.

With just a few taps on their ServiceTitan app, the engineer can show the customer any potential system upgrades and tell them exactly how much it’ll cost using the Pricebook's detailed descriptions and images.

Over to You!

HVAC diagnostic charts are valuable tools for field technicians. They help identify common problems such as incorrect charge levels, malfunctioning condenser fan motors, capacitor faults, filter blockages, and more. This makes the job diagnosis much faster. 

While helpful, HVAC diagnostic charts don’t give you the complete picture. You’ll need specialist knowledge to diagnose and fix more complex issues.

ServiceTitan enhances HVAC servicing by letting technicians directly access diagnostic charts and job history on their mobile devices. This leads to faster, more accurate repairs and happier customers.