Dial equipment existed long before the perfection of air conditioning for large buildings, so I presume step-by-step, panel, and crossbar switches did not require air conditioning. I presume that the heat generated by relays, ringer motor generators and the like was not great enough to cause worry. Most old telephone buildings had big windows.
However, in the late 1930s, carrier systems and long distance routes using electronic gear was installed. These used vacuum tubes which generated a lot of heat. Did switching buildings that had such gear have any special ventilation or early a/c to remove that heat*?
In the 1950s electronics continued with the implementation of microwave systems. Likewise, did amplifiers require air conditioning in those buildings?
I believe ESS offices were always air conditioned. Indeed, the literature states a failure of an early ESS unit was due to air conditioning failure, not the switch itself.
As an aside, one of the Western Union Technical Bulletins housed on this site has an article about how WU air conditioned one of its buildings in NYC.
Air conditioning for buildings was perfected in the late 1930s though its use grew very slowly. A couple of buildings built during WW II in DC were air conditioning, I don't know how people survived DC's hot humidity in non a/c buildings. Technical advances and efficiency in the early 1950s allowed it to be more widespread and home window units came out at that time.
I think a Bell Labs facility built around 1940 was built with air conditioning. I think the Pentagon had a/c when built.
*The labs where the Univac was developed were not air conditioning and the workrooms were extremely warm. Engineers ran around in their underwear and rules were posted requiring them to put their clothes on when entering the outer offices. In contrast, IBM's labs of the same era were air conditioned (since the 1930s). IBM's people had to wear suits, but when entering IBM's front offices in those days they had to use old fashioned starch collars favored by Thomas J. Watson Sr, president. Interesting contrast between the two computer companies -- suits vs. underwear. In a visit to a Univac facility in
1978, it was clear they were still much more informal about dress (colored shirts and the like) than an IBM facility of the same time -- white shirts only.
[TELECOM Digest Editor's Note: Interesting you wrote about this today when the outside temperature here in Independence reached 106 degrees; the hottest for this year so far. My air-conditioning has been running almost continuously for the past two days. I do not know how I survived back in the 1950-60s when the places I worked did not have a/c nor did I have it at home until around 1968 or so. PAT]