T-R PHOTO BY ROSS THEDE The Marshalltown Fire Department responds to a fire and explosion shortly after 2 a.m. Thursday morning which caused extensive damage to two homes on Sixth Street. The fire is believed to have been caused by an air conditioning unit.

A cooling device became way too hot in the early morning hours of Thursday.

Shortly after 2 a.m., the Marshalltown Fire Department received a call about a fire at 7 1/2 S. Sixth St. Upon arrival, Chief David Rierson said flames were licking up the side of the home from where the air conditioning unit was. The air conditioner then exploded, and the flames from that outburst caused the house next door — 9 S. Sixth St. — to catch fire, as well.

It is estimated the house at 7 1/2 S. Sixth Street sustained $30,000 in damages. Next door, that house received $4,000 of damage.

Rierson said eight firefighters responded with two units. Nothing other than water was used to extinguish the fire, which they accomplished in a little more than two hours. There were no injuries among the residents or the firemen.

“Nobody was hurt and that is what is important,” he said.

Rierson said he had never known an air conditioning unit to start a fire, much less explode.

“You know, there’s freon gas in there,” he said. “When a gas gets hot enough, it will vaporize and explode. We never saw one do it before but we witnessed it first hand last night.”

Rierson urged Marshalltown residents to keep their air conditioning units serviced. He said make sure the condensing unit is free of dust and dirt. When a unit becomes clogged with dirt and dust, it can restrict air flow, which leads to overheating.

Chad Gauthier, owner of B&G HVAC in Marshalltown, said he has never heard of an air conditioner catching fire and exploding, but speculated it could happen. He said if oil was leaked and interacted with the capacitor, it could. If a condensing unit becomes clogged, Gauthier said the unit is more likely to freeze up.

“A clogged condensing unit should not lead to fire, but they should be kept clean for maximum efficiency,” he said. “People can clean them at home with the proper care. You don’t want to damage the unit. Use a light-pressure garden hose.”

Having a yearly unit checkup is also important, Gauthier said. Any maintenance problems can be readily diagnosed and treated before the warm summer months begin. One of the more common annual problems is the presence of rodents or snakes in the unit, which he said can chew up the wires.

Gauthier reassured an air conditioner catching fire or exploding is a rare occurrence.

“I have never seen it happen. It would be interesting to see what caused this one,” he said.