Why Air Compressors Overheat in Summer and How to Prevent It

Summer is the peak season for air compressor shutdowns. High-temperature shutdowns — where the compressor's thermal protection trips and shuts the unit down to prevent damage — spike in July and August across Midwest industrial facilities. The causes are predictable, the prevention is straightforward, and the cost of not addressing them is significant: unplanned downtime, potential compressor damage, and production disruptions at the worst possible time. This guide covers why compressors overheat in summer and exactly what to do about it.

Maintenance

Why Summer Is Different for Air Compressors

Air compressors are heat engines — they convert electrical energy into compressed air, and the compression process generates substantial heat. Cooling that heat away is the compressor's job, and it relies on a temperature differential between the compressor and the ambient air to do it. When ambient temperatures rise from a typical winter 50°F compressor room to a July 95°F compressor room, the cooling capacity of the system drops significantly — the temperature differential driving heat rejection decreases, and the compressor runs hotter.

Most rotary screw compressors are designed for optimal operation at ambient temperatures up to 95–100°F. When the compressor room exceeds those temperatures — which happens in unventilated or poorly ventilated equipment rooms in midsummer — the thermal safety system activates and shuts the unit down.

The Most Common Causes of Summer Overheating

Dirty coolers. The aftercooler and oil cooler are the primary heat rejection components in a rotary screw compressor. Dust, lint, and airborne debris accumulate on the cooler fins over the course of a year, reducing airflow and degrading cooling efficiency. In summer, a cooler that was marginally adequate in cool weather simply cannot keep up. Clean cooler fins are the single most effective prevention for summer high-temperature trips.

Inadequate compressor room ventilation. Compressors reject heat into the compressor room through their coolers. If that heat cannot escape the room — because ventilation is inadequate or blocked — the compressor room temperature rises throughout the day until it exceeds the compressor's design limit. Proper compressor room ventilation requires enough air volume to remove the compressor's heat output and maintain room temperature within the compressor's operating range. Many compressor rooms are chronically under-ventilated.

Low oil level or degraded oil. Compressor oil is the primary cooling medium inside the compressor. Low oil level reduces the system's heat absorption capacity. Degraded oil — broken down from extended service or contaminated with water — has reduced heat transfer capability. Check oil level and condition as part of summer preparation.

Worn or failed thermostatic valve. The thermostatic mixing valve (also called the thermal bypass valve) controls oil temperature by mixing hot oil from the airend with cooler oil from the cooler to maintain target oil temperature. A failed or stuck thermostatic valve can cause the compressor to run with either excessively hot oil (if it fails open, bypassing the cooler) or excessively cold oil (if it fails closed, always routing through the cooler — which causes moisture condensation in the oil). A thermostatic valve that fails to fully open in summer heat is a common cause of high-temperature shutdowns.

How to Prevent Summer Overheating: The Checklist

These are the specific actions that prevent the majority of summer high-temperature shutdowns:

Clean cooler fins thoroughly in May or early June, before temperatures peak. Use compressed air to blow debris from the fins — work from the clean side to push debris outward, not deeper into the fins. For facilities with heavy airborne contamination, clean monthly through the summer.
Verify compressor room ventilation is working properly. On a hot day, measure the temperature inside the compressor room versus outside. If the room is more than 5–10°F warmer than outdoor ambient, ventilation is inadequate. Check that ventilation louvers are open, exhaust fans are running, and ducting is directing hot discharge air out of the room rather than recirculating it back to the compressor inlet.
Check oil level and perform an oil change if oil is due or degraded. Summer is not the time to run on marginal oil. Change oil according to the manufacturer's schedule — do not extend intervals during high-ambient-temperature operating conditions.
Test the thermostatic valve. This is done by monitoring compressor discharge oil temperature and comparing it to specification. A Brabazon service technician can diagnose thermostatic valve function as part of a PM visit.
Check air/oil separator differential pressure. An overloaded separator element increases the pressure and temperature throughout the compressor system. Replace separator elements that are at or approaching the manufacturer's differential pressure limit.

What to Do When Your Compressor Trips on High Temperature

If your compressor has shut down on a high-temperature fault, do not immediately restart it. Allow it to cool for 15–30 minutes, then investigate before restarting. Check the compressor room temperature, inspect the coolers for obvious blockage, verify oil level, and check for any visible signs of the cause. If the compressor trips again shortly after restart, do not continue cycling it — call for service. Repeated thermal cycling caused by compulsively restarting an overheating compressor accelerates oil degradation, stresses seals, and can cause permanent damage to the airend bearings.

Brabazon's service team provides emergency response for compressor failures throughout the Midwest. If your compressor has shut down on a high-temperature fault and you cannot identify the cause, our factory-certified technicians can diagnose and repair the issue — with parts inventory available for Sullair and all major compressor brands.

Related Resources

Preventive Maintenance Agreements — summer prep is a standard part of Brabazon's PM programs
24/7 Emergency Repair — when an overheating shutdown happens during peak production
Spring Compressed Air System Checklist — prepare your system before summer heat arrives

Get a Summer Service Check