It doesn't work that way. While there may be some patterns to what "up" adds to verb, it's probably much more reliable to simply learn the compound verbs verb at a time, as independent verbs that happen to have at least some degree of relatedness through a morphological root.

This might make it easier to keep up, and to not give up or f- up or blow up in learning English. Anyhow, I'd better shut up and simply suggest, I wouldn't take up this approach.

Otherwise, you might end up to regret it.

In both of your examples, I don't interpret the word "up" as modifying the verb. Instead, it refers to the location where the action is happening. For example:

• "There's probably something trapped up in their ventilation system"
  • In this sentence, the word "up" is referring to the fact that the ventilation system is above where people would usually be. So, the word "up" is simply stating that the ventilation system is located above something else
  • To make it more clear, it's not: "... something trapped up in their ventilation system" - instead, it's "... something trapped up in their ventilation system"
• "The other three scouting up the hallway"
  • In this case, the word "up" can be used to mean "further". Basically, it's saying that the other three are scouting at a location further along the hallway
  • Again, instead of "the other three scouting up the hallway", it's the other three scouting up the hallway"

In both sentences, the word "up" isn't modifying the verb - instead, it's talking about the location that comes after the verb.

However, the word "up" can also be used in the way you found online. For example:

• "I'm cleaning the house" can also be expressed as "I'm cleaning up the house"
  • Both sentences have essentially the same meaning, just phrased differently and with a little more emphasis.