Harvey Norman Fyshwick warehouse manager Robert Mason said 33 portable air conditioners were sold on Monday and about 120 had been sold since Saturday.

"These portables are what's walking out the door," he said.

Mr Mason said 100 more portable units had been ordered to meet the continuing demand during the hot weather.

The retailer's installer is booked out until the end of the month as Canberrans snap up air conditioning units that were brought into the warehouse on 40 pallets at the beginning of summer.

"Every year we'll get 100 or 200 [air conditioners] in, and by the end of the summer they're gone," Mr Mason said.

Calls placed by The Canberra Times to air conditioning retailers and installers met with engaged signals and hold music.

A staff member from Proactive Airconditioning, which installs and services domestic and small business airconditioning units, said the business was very busy and its team was booked out for the rest of the week.

"There's a lot of breakdowns," she said.

"You're getting very disgruntled people. They don't like to wait [to have their units repaired]."

She said the team couldn't install roof top evaporative coolers when day time temperatures were high and that unless it was early in the morning, it would have to wait.

But it was usual to have increased demand in summer, she said.

"The same thing happens in winter, when we get a cold snap."