(this story has been updated)

Two people died in Montgomery County after the 911 system failed there Sunday night, and authorities said they want to know if the deaths could be linked to the two-hour shutdown.

“I am calling for an immediate investigation into the outage and what impact it may have had on the County’s response times to emergencies — as well as any consequences,” County Executive Ike Leggett said in a statement.

He said he wanted the 911 support systems thoroughly checked to be sure they had adequate stability and resilience, asserting that residents “must be able to count on” prompt emergency response.

The county said 911 service was out from about 11:10 p.m. Sunday to 1:09 a.m. Monday. Callers received only a busy signal. The public was advised to call individual police stations or firehouses. The county said it made notification through social media and the Alert Montgomery emergency information system.

During the outage, a county statement said, fire and rescue units “responded to two medical emergency calls” involving deaths. One was that of a 91-year-old Olney woman, and the other a 40 -year-old man from Twinbrook. It was unclear if the outage was involved.

“We don’t know that yet,” said Patrick Lacefield, chief spokesman for the county. “We are gathering information” he added. “We want to know whether it could have made any difference.”

Pete Piringer, spokesman for the county fire and rescue service,said he did not immediately know if either person was transported to a hospital.

The 911 outage was traced to a malfunctioning HVAC system, Lacefield said. He said the malfunction caused the backup system to shut down. “For some reason,” he said in an interview, that in turn shut off the main 911 communications server.

Authorities were still trying to determine why the server was affected by the backup system, he said.

He said full 911 service was restored Monday.

Normally, the emergency center receives about 650 calls a day, Lacefield said, but the hourly numbers are smallest during the period at which the outage occurred.

The malfunction occurred at the county’s alternate emergency communications center in Rockville. It had been placed in service about two dozen days ago so equipment changes could be made at the main emergency communications center in Gaithersburg.

It was not clear what if any role in the outage was played by the shift.