The heater not working in a 2000 dodge ram 1500

[Erik the mechanic]

So I just bought a 2000 dodge ram 1500 with 121000 miles on it and it does but doesn't have heat working properly and I'm stumped. I've looked into it and all my actuators are working and relays are working properly as well as the fan and climate controls on the dash no check engine light but it keeps using the bypass valve when accelerating and I can't figure out why. Its full on coolant as well as having no rust in the coolant. Any advice is much appreciated

 

[Grams]

Have you attempted to blow thru the heater core? There are SOME Rams which suffered from “sand” in the heater core blocking coolant flow.
This was apparently due to “casting sand” left in the engine-block when it was cast.
Numerous “flush” operations have been needed by some owners.