A modern air conditioning unit is a complex piece of machinery. It contains several sensitive components such as relays, switches, and controllers that ensure the entire system is working properly. These parts are quite sensitive so they operate at a lower voltage – 24 VAC.
On the other hand, major system components, such as a draft-inducing fan, require more juice. More precisely, they require the standard 240 VAC.
An air conditioning unit uses an HVAC transformer to drop the voltage down to where more sensitive components can operate properly.
Needless to say, if the HVAC transformer malfunctions, the circuit breaker will trip to prevent further damage. This means that you will be stuck without air conditioning, which can be a major problem, especially in the summer.
So without further ado, we bring you a troubleshooting guide that will help you determine if your HVAC transformer is fried or if something else needs to be addressed.
Disclaimer: this is not a guide for beginners. A transformer failure is not a simple issue to fix or troubleshoot by yourself, if anything in this guide seems outside of your skill level, we recommend you call an experienced HVAC technician.
1. Find out if there was a power surge
Many people overlook this step. However, a power surge is the most common cause of a fried HVAC transformer. This is especially true for newer units that are often more sensitive to power blips. If you suspect this is the cause of your problem, locate the transformer inside of your air handler and get to work.
Follow these steps:
1. Inspect the components visually. If you notice parts like capacitors looking fried, you probably had a major power surge.
2. Shut down the system.
3. Check and reset the breaker
4. Wait around half an hour before restarting the system
5. If the breaker trips again, that’s all the evidence you need that there’s been a power surge.
Unfortunately, this is a serious issue and a lot of parts will probably need replacing, so you’ll have to call an HVAC professional.
2. Check the indoor fan
This fan moves the air into your living space so the heat transfer cannot happen if this part stops working.
The major issue here is that a faulty HVAC transformer could be just one of the causes of an inoperative fan, so pinpointing the real culprit will probably be quite tricky. However, there are a lot of symptoms that can point to a failing transformer.
Transformers usually make some noise, but if the noise is louder than usual and you notice a lot of vibration along with a non-functioning fan, your HVAC transformer might be bad.
The process is as follows:
1. Check for loose connections and signs of overheating such as discoloration.
2. Use a voltmeter to check the voltage, current, and kVa. Compare those numbers with the ones written on the transformer’s nameplate, and if you spot any discrepancies you’ve got an overload.
3. Check the outside unit condenser, fan, and compressor
These three components help the refrigerant circulate through your system. First, the compressor compresses the refrigerant and discharges it as vapor. As the fan blows across the condenser it eliminates the heat from the refrigerant, which then changes back into liquid.
Here’s how to troubleshoot these parts:
1. Since the compressor requires a supply voltage within 10% of the manufacturer’s recommendation, check for voltage at the breakers, switches, fuses, and disconnects first.
2. Inspect the low-voltage transformer. If you get a reading lower than 21.5 volts, there won’t be enough power to activate the contactor and start the compressor.
3. Check if the run capacitor is working properly. If this part is faulty the motor can draw in too much current, which can cause the unit to overheat.
These components wouldn’t work at all if the HVAC transformer was faulty. So if any of these do work, you’ll need to shift your focus elsewhere instead of troubleshooting the transformer any further.
4. Check the power to the primary side of the HVAC transformer
The next step is examining the power going into the step-down transformer. If there is a 240v feed into the primary side of the transformer, it means that the main power going into the unit is not to blame. On the other hand, if the reading isn’t 240v, you’ll need to troubleshoot other components.
Here’s how to check this side of the HVAC transformer:
1. Measure the voltage at the proper terminals
2. If you’re not getting voltage on this side, you need to check the breaker and wiring going into the unit for damage, corrosion, or loose connections.
5. Check the voltage at the secondary side of the HVAC transformer
Since we’re talking about the step-down transformer, the voltage going in on the primary side should be 240v and the voltage on the secondary side should be 24v. If the voltage on the primary side checks out, but the voltage on the secondary side is showing 0v, it means that the HVAC transformer is officially at fault.
Here’s how you can troubleshoot this side:
1. Identify any open or short circuits, loose wiring and connections, and dirty wiring.
2. Turn on the system and check for vibration, hum, or noise.
6. Check the contactor
This important part is controlled by the thermostat and governs the flow of electricity to all components in the system. The coil terminals are energized by receiving voltage from the thermostat, which pulls in the contacts that allow the main power at both incoming circuit wires to be applied to the fan motor and the compressor to the top terminals.
However, a contactor can get stuck if the surfaces inside become pitted and oxidized. Once that happens, the current will flow to the specific components constantly instead of cycling on and off.
Here’s how to troubleshoot a contactor:
1. Turn off the power to the unit.
2. Lift the metal cover and find the wiring connections on the condenser unit.
3. We recommend taking quick photos so you know how to reconnect every wire.
4. Start with the contactor coil connection and measure for 24v. If the reading is 0v, it means that the contactor coil isn’t receiving any power.
5. Find the line wires of the contactor and measure for 240v and if the reading is 0v, there is no main power. In that case, check the fuses or the breaker.
6. Next, switch your focus to the load side of the contactor and measure for 240v at the T1 and T2. If the measurement is 0v, it means that your contactor is broken and if you spot a voltage drop of over 3% across the contacts, the contacts themselves might be damaged.
When should you call a professional?
Even if you’re quite handy with gadgets like voltmeters and multimeters and you know how to tinker with electronics, HVAC systems are a different beast. They’re quite complex and even if you do manage to get down to the bottom of the problem, you will most likely have to call in a professional at some point.
After all, you don’t want to hurt yourself or your HVAC system, for that matter.
If you think you have a problem with an HVAC transformer or any other complex electronic component, call Aztil AC – a leading air conditioning company in South Florida.
We can help you with everything related to your air conditioning system quickly, efficiently, and at any time of day (or night). We’ve got a team of experienced HVAC technicians that can diagnose and fix your transformer in record time.