Reddit reviews Redline Detection 95-0700 SmartFit Universal Cooling System Test Kit with Pump

Ahh, heating issues, sometimes very easy, sometimes the most difficult thing to do on a car.
There are many things that can cause your heater to not work.

Firstly, most heater issues are caused by low coolant or trapped air in the system so fill it to the rim and burp it. If its low, its going somewhere, so find it.

Next, its often the heater valve, the mixers, wiring or vac lines. (I doubt your car has vacuum controlled conditioning system though)

But, if you have narrowed it down to the core its self, first thing to do is to try to blow it out by bringing your engine to redline a few times on the highway. (First thing to do for most issues on a car, "A redline a day keeps the mechanic away") If that doesn't change anything, then its time for a flush. Set the car heat to high, unhook the core inlet and outlet hoses on the engine, then flush and backflush it a few times with a garden hose. If you have low flow, you can pour CLR in the hoses and let it sit for a few hours then flush it again.

If it hasn't had one recently, now is definitely a good time for a full coolant flush too.

Helpful tools I would recommend for the job:

Airlift ~$80 (Very helpful for burping a system)

Coolant System Pressure Tester ~$150 (Helpful for finding leaks and testing the cap)

Refractometer ~$50 (A very helpful tool, especially if you live in a cold climate. It measures the freezing point of ethylene glycol, propylene glycol and measures battery acid state)

As far as recycling the coolant, in some counties you can pour it down the drain when properly diluted, but most of the time you have to bring it in to a recycling center.

Good luck! If you have any further questions, ill be around.