Why Your Compressor Trips on Hot Days

Every summer we get the same call: 'My compressor's been fine all winter and now it's tripping every afternoon. What's wrong with it?' Usually nothing's wrong with the compressor. The compressor is doing its job in conditions it was never installed to handle.

What's actually happening

A rotary screw compressor produces about 2,500 BTU of heat per HP per hour. A 25 HP unit dumps 62,500 BTU/hour into whatever room it sits in. In winter, that heat goes out through the building envelope. In summer, when ambient temperature is already 85°F and the compressor room hits 110°F, the compressor's internal cooling system can't reject enough heat fast enough.

The high-temperature shutdown switch trips at 220°F oil temperature on most modern rotary screws. The compressor shuts down, cools off for 20 minutes, restarts, and runs until it overheats again. By 3 PM you're cycling on and off every 30 minutes and your shop is out of air.

Fix 1 — Cool intake air

The compressor inhales ambient air through its intake. That air becomes the working fluid the compressor compresses. Hotter intake = hotter compression = hotter discharge. If your compressor sits in a closed room, the room heats up, the intake air gets hotter, and you're chasing your tail.

• Duct intake air from outside the compressor room — cooler, drier, and isolated from the heat the compressor is producing.
• If outside ducting isn't possible, run a louver between the compressor room and a cooler space (warehouse, shop bay) so cool air replaces what the compressor pulls.
• Avoid putting compressors in small unventilated mechanical rooms. They cook themselves.

Fix 2 — Exhaust the heat

The compressor's cooling fan blows hot air out the back of the cabinet. That hot air has to leave the room or it just recirculates. Install an exhaust fan or a duct that pulls compressor exhaust outside. In winter, the same setup can be reversed to use the heat for shop space heating — heat recovery is a free byproduct.

Fix 3 — Clean coolers

Rotary screws have an oil cooler and an aftercooler. Both are heat exchangers with fins that get clogged with dust over time. A 50% clogged cooler can drop heat-rejection capacity by 40%. We see compressors that haven't had the coolers cleaned in five years — the metal looks black with dust.

Annual cooler cleaning is cheap and pays back the first hot afternoon. We typically clean coolers as part of preventative maintenance — but if you've never had it done, schedule it before summer hits.

Fix 4 — Check ambient temperature spec

Standard rotary screw compressors are rated to 110°F ambient. Some are derated to 104°F. If your installation routinely sees ambient temperatures above the rating, the compressor will overheat regardless of cooler condition or ventilation. The fix is either an upgraded high-ambient package or a relocation to a cooler space.