Do the same for the radiator pipes and also plumbing pipes in kitchen and bath.

If that's okay then check the coil.Look for dents and dings to the fins and straighten them out.Turn the unit off outside and run a house through fins to clean out the coils.Gets grass and dirt out of there.Make sure there are no obstructions around the unit where it can't breathe.Then after cleaning turn back on and put a dollar bill to the fins all around.The bill should stick if air flow is good.If there is a section where the bill isn't sticking it needs cleaning for good suction.The reason this is important is just like a radiator the hot air is brought out to the pump and cooled through the fins before it goes back into the house.If the air flow isn't there to coll properly then the air won't be cold enough.I hope this helps.The reason I know so much about this as I went through this on my personal residence.Here in Georgia it has been 95 to 100 almost every day for the last 2 to 3 months.Can't wait for it to end.

Your enthusiasm and positivity radiate from everything you do!

I grew up in a house with radiators and it did have a valve that could be adjusted so maybe not a big deal?

BUT if you are keeping the units for rentals, and have a hot water BOILER, by all means keep the radiators/baseboards that go with it, install a combi boiler (Navien or similar) that combines hot water for heating with hot water for showering.

Clean common area and collect my washing machine quarters.6 months I change the batteries in the smoke detectors/CO, fire extinguisher inspection/charging6 months I do a plumbing inspection6 months I do a thermostat battery changeNovember I do a radiator bleed.None are done at the same time and I do a complete walk through when doing.My buildings are across from town hall and the police station.

We do have a metal roof, which is one thing to consider because there is no attic space the roof can't radiate that heat into the attic and then allow it to vent so the exterior roof temperature tends to be something like 15-25 degrees higher than a roof on a normal attic.

Not only does it create a bleak look; it also adds heat that can radiate and kill plants, make patios uncomfortably hot, etc. 

Is that the only radiator in the room?

Is the heating system forced air or radiators?