Dozens of city employees working out of the Frank F. Fasi Municipal Building went home early Monday after air conditioning to the building could not be turned on.

No customer services were affected by the situation, city officials said.

A 400-ton chiller unit failed to fire up due to “internal issues” when a crew tried to turn it on at 4:20 a.m. Monday, city Facility Maintenance Director Ross Sasamura said.

City officials do not know how many people went home since it was up to department heads to decide who would stay or go, he said.

The building, located at Alapai and South King streets, houses most of the city’s agencies.

The city has two, 400-ton chillers. The backup chiller, however, could not kick in because it had been put out of service earlier for a scheduled preventive maintenance day, Sasamura said.

That second chiller will be ready to go Tuesday morning, he said. City officials are still trying to determined what caused the first chiller to malfunction but are hoping it too can be repaired by sometime Tuesday.

A smaller, backup 100-ton chiller was used to keep air conditioning going in the basement offices of the city Department of Emergency Management, which is tasked with dealing with disasters on Oahu including earthquakes and tsunamis.

In an unrelated development, the city’s Kapolei Hale failed to have air conditioning for several hours Monday before it could be turned on at 9 a.m. Sasamura said that was caused by a computer glitch.