Why is it not getting cooler, just hotter

You have already been told that there is a VALVE in control of your heaters water flow...THE OTHER NAME of the heater core is a heat EXCHANGER... It delivers HEAT to the passenger compartment... In so doing the water returning to the ENGINE will... BY THE NATURE of plain/pure PHYSICS, be cooler...!!

The (unstated but) very SIMPLE question here...
The heater is NOT working...??
Check the VALVE.

You already know where the water goes in... and comes out There's no need to remove the core for FLUSHING.

One (return) heater hose being cooler is as normal as the sun rising in the EAST (it is not a problem... by itself)...

Carnac the Magnificent

there might be a broken hot water pipe somewhere and so that might be causing the heater to stay on as its not getting to temperature.

evaporative coolers use a principle of blowing air though a filter that is water moist
the air passing through the water uses a heat exchange process as the water boils off, the air is cooled and so you get cooler air
very efficient in places where the humidity is under 80% but over that the water doesn't evaporate all that readily and so the effectiveness is reduced
basically the hotter the day and the lower the humidity the more efficient they are.
Cheap --yes as it only runs a small motor for the fan and an even smaller motor for the water pump, but you will need a regular water supply some units have a small tank which needs regular filling and others can be connected to the home water supply
it is not an air conditioner , simply an air cooler.

If you've noticed water pooling on the floor of your Vinotemp cooler, you're not alone. This is a common issue that can be caused by a few different things. The most likely culprit is a blocked drain. If the drain is blocked, the water won't be able to escape the cooler and will instead pool on the floor. To fix this, you'll need to unblock the drain. Another possible cause is a faulty seal. If the seal isn't working properly, it can allow water to escape the cooler and pool on the floor. To fix this, you'll need to replace the seal. Finally, it's possible that the water is coming from the condenser. If the condenser is leaking, it can cause water to pool on the floor. To fix this, you'll need to replace the condenser. No matter what the cause, it's important to address the issue as soon as possible. Otherwise, you could end up with a flooded cooler and a lot of ruined wine!

Using one cup of bleach Per 5 gallon jug. Find the drain plugs on the bottom of the unit there are two. Drain unit of any water that is in it now. Replaced drain plugs. Place 5 gallon jug on top of unit and allow unit to fill. Be sure that heated water is off. Open spigots and allow a gallon of water to drain. After about 15 minutes open the drain plugs and allow all of the solution to drain out. Proceed to fill the 5 gallon jug with clean Clear filtered water and allow that to drain thru the unit, do this five more times.

If the water seems hotter than normal, then a faulty thermostat would be a good bet.
If water doesn't seem any hotter than normal, then check incoming water pressure.
usually 2 things cause that, too much pressure coming in, or thermostat faulty and not cutting out when normal temperature reached, thus higher temperature, and pressure. If both them check out, replace valve.

Yes it can. The car will not get up to operating temperature as fast. It's never good to modify a car from its original factory specifications.

If you have a hot water supply then use it otherwise use a Y hose to connect the cold supply to both hot and cold inlets. Machines are generally made with cold only inlets today as most washing detergents are formulated for cooler washing temperatures and the mfrs say that it is more convenient and cheaper to heat what is required rather than draining your domestic hot water tank. There will not be a problem with using cold fill to both inlets but you can expect some of the hotter was programmes to take longer than expected as the water will have to be heated in the machine to allow the programme to run correctly.

pull the handle off and there is a black dial you can pull out and readjust on the shaft of the cartridge that will allow you to have cooler and hotter settings. it's black plastic and has little splines on it . the more you go one way the hotter it gets and the same the other way gets cooler

It may be that the thermostat is not the proper one needed to regulate heater temperature operation. Check the thermostat. It may be rated lower than necessary to allow for heating purposes. And if you dare, you might try (for winter purposes only) installing a thermostat of a higher rating so the coolant will need to run about 20 degrees hotter before opening and thus making the heater core a bit hotter to facilitate better heating, if you can locate a thermostat of the same size that is which will fit a Sportage housing.
It seems to be determined that the core is not plugged or else this would have been my first bit of advice for you to address. If youre determined to continue with your own retrofit core make sure the housing you install it is sealed to allow your fan or blower to pump this heated air into the vehicle and not outside into the engine compartment. I hope this might prove useful to your endeavor, good luck.