Deira apartment AC runs constantly and the bills are brutal — is it the old units or the building?

Constant running is almost never one single cause in these older Deira blocks, it's usually an under-maintained unit AND a building that leaks heat, and the cheapest wins are on the building side. A properly serviced AC that still never cycles off is normally being defeated by heat coming in faster than it can remove it: unsealed flat doors, single-glazed windows in direct sun, and long uninsulated runs are the usual culprits in old stock. So do it in order: first a real service on each unit (coil clean, gas check, thermostat calibration) so you know the AC itself is delivering, then the low-cost envelope fixes, door seals, blocking harsh afternoon sun, checking the AC pipe insulation. That combination cuts runtime far more than swapping to a new unit that then fights the same leaky room. Putting the flats on a scheduled AC servicing in Deira plan also stops the slow drift where efficiency quietly falls and the bills creep up unnoticed between tenants.