How to Diagnose a VFD Tripping on Overtemperature
When a drive trips on its own overtemperature, it is protecting its power electronics from heat they cannot shed, and the cause is almost always a cooling problem, an environment problem, or the drive being worked harder than its conditions allow. This is the drive overheating, not the motor. This page is for the technician facing a drive that keeps posting an overtemperature fault. It works the causes in order, from a failed cooling fan and blocked airflow to a hot enclosure, a high carrier frequency, and a load that exceeds what the conditions permit.
VFD Overtemperature Trip in one line: A VFD overtemperature trip means the drive's own heatsink or internal temperature exceeded its limit, so work the causes in order: a failed or dirty cooling fan and blocked heatsink airflow, a hot ambient or an unventilated enclosure, a carrier frequency higher than the conditions support, and finally a load pushing more current than the derated drive can carry. Confirm the cooling fan runs and the heatsink and vents are clean first because those are the most common and cheapest, then check the environment and the settings before concluding the drive is undersized for its conditions.
First Checks: Cooling Fan and Airflow
Start with the drive's own cooling, because a stopped or choked fan is the most common cause and the easiest to confirm. Most drives cool their power stage with a fan pulling air across a heatsink, so verify the fan actually spins when the drive is running and warm, and that it moves air the right way. A fan that has failed, seized, or is turning slowly lets the heatsink climb until the drive trips, and a fan is a wear item that fails predictably over service life.
Clear the airflow path through the drive. Dust caked on the heatsink fins, a clogged intake filter, or debris blocking the vents all strangle the cooling even with a healthy fan, so inspect and clean the heatsink and any filters. A drive mounted with too little clearance above and below, where the cooling air enters and leaves, is starved the same way, so confirm the installation left the manufacturer's required spacing. Restoring clean, unobstructed airflow often clears the trip on the spot.
Confirm the trip tracks heat and load, which points at cooling rather than a sensor fault. An overtemperature that appears after the drive has run a while under load, and clears after it cools, is a genuine heat problem. One that trips instantly on a cold drive is more likely a failed temperature sensor or a drive fault, which is a different diagnosis. Noting whether the trip follows the drive warming up tells you whether to keep chasing cooling or suspect the drive's own electronics.
Ambient, Enclosure, and Carrier Frequency
If the fan and airflow are good, look at the environment, because a drive can only shed heat into air that is cool enough to take it. A hot room, direct sun on a skid, or an enclosure with no ventilation raises the air temperature around the drive so it cannot cool, and it trips at a load it would carry easily in a cooler spot. Measure the air temperature at the drive intake against the drive's rated ambient; if the air is hotter than the rating, the environment is the fault, the same enclosure-heat problem covered in the page on cabinet heat dissipation and IO derating.
Check the enclosure specifically, since a sealed cabinet traps the drive's own heat. A drive in a closed enclosure heats the air inside it, and without ventilation, a cooling fan, or air conditioning that inside air climbs well above the room. A cabinet that was adequate when the drive ran light can overheat once the load or the ambient rises, so confirm the enclosure actually removes the heat the drive produces rather than just containing it.
Weigh the carrier frequency, which the drive itself produces heat in proportion to. A higher carrier frequency, described in the page on VFD carrier frequency, increases switching losses and drive heat, so a carrier set higher than the conditions support can push the drive into overtemperature. If the application does not need the high carrier, lowering it reduces the heat directly. This ties into derating, since the same conditions that force a carrier or ambient derate, covered in the guide on derating a VFD, are the ones that cause an overtemperature trip when ignored.
Load, Derating, and When the Drive Is Undersized
When cooling and environment are sound, check whether the drive is simply carrying more current than its conditions allow. Every drive's usable current falls with a higher carrier, a hotter ambient, and higher altitude, so a drive sized on its nameplate current without applying those deratings runs hot and trips on overtemperature under a load that looks within its rating on paper. Compare the actual running current to the drive's derated capacity for its real conditions, not to the nameplate figure.
Rule out an intermittent overload feeding the heat. A load that has grown, or that surges periodically, drives the current up and the drive hot, so a drive that overheats only when the process is heavy is telling you about the load, not itself. Trace whether the current has crept up over time, which points at a developing mechanical problem or a process change, before concluding the drive itself is at fault. The motor-side of a growing load is covered in the guide on diagnosing a motor running hot.
Conclude the drive is undersized only after the rest is clean, and then fix it correctly. If the fan works, the heatsink is clean, the ambient and enclosure are within rating, the carrier is reasonable, and the load is normal yet the drive still overheats, the drive is genuinely too small for its conditions, and the answer is a larger drive, a lower carrier, or a better environment, not defeating the protection. Because the drive's temperature and load are values a monitoring system can trend, a drive creeping toward its thermal limit as conditions drift shows in the data, letting the fix be planned before the overtemperature trips start stopping the process.
Frequently Asked Questions
Is a VFD overtemperature trip the drive or the motor overheating?
It is the drive itself, specifically its heatsink or internal power electronics exceeding their temperature limit, not the motor. A separate motor thermal trip covers the motor. Because it is the drive overheating, the diagnosis focuses on the drive's cooling fan and airflow, the ambient and enclosure temperature, the carrier frequency, and whether the load exceeds the drive's derated capacity. If the motor is what is running hot, that is a different checklist focused on the motor's own cooling and load.
Why does my VFD overheat only in summer or on hot days?
Because a drive can only shed heat into air cool enough to accept it, and a hotter ambient leaves less margin. On a hot day the air around the drive rises toward its rated limit, so a load it carries fine in cooler weather now pushes it over into an overtemperature trip. Measure the air temperature at the drive intake against its rated ambient. If the air is too hot, the fix is cooling or ventilating the space, relocating the drive, or derating the load for the real ambient.
Can lowering the carrier frequency stop overtemperature trips?
Often, yes. A higher carrier frequency increases the drive's switching losses and internal heat, so a carrier set higher than the conditions support can push the drive into overtemperature. If the application does not need the quieter motor or smoother waveform the high carrier provides, lowering it reduces the drive's heat directly and can clear the trips. This is the same relationship that forces a carrier derate, so lowering the carrier both cools the drive and recovers usable current capacity.
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