'Am afraid if I pay the bill now, they'll stop being responsive."

I agree but you should promptly pay all but a couple hundred dollars and let their office know what you are doing. Unless the warranty ties you to the installer,you might think about calling somone else down the line. It's not very reassuring that they can't troublshoot such simple issue.

They should not even give you the final bill. Most time 100% payment at COMPLETION, How do you know the bill is correct at this stage, job not done yet.

I agree with Klem1. It sounds like something is not wired properly and the installer can't figure it out. You may have other installation problems and not yet know about it.

My advice is you call the billing department and let them know you intend to pay the full amount of the bill when everything is working to your satisfaction. I would not pay anything now. Withholding a few hundred dollars in not enough of an incentive to continue working on the problem.

I wouldn't hold back 100%. I think that sends the wrong message. Maybe 50%. Let's be reasonable as well as give dealer incentive to straighten out all issues.

IMO

"Am afraid if I pay the bill now, they'll stop being responsive."

That's how it works 90% of the time.

Don't pay more than 3/4 of the bill until everything is completed to your total satisfaction.

I think you are going to find that the cassette unit in your bedroom is operating as designed. A unit installed in the ceiling has to continue to operate to "sample" the air in the space. Otherwise you would end up with "stacked" temperatures. This is not what we are used to in hvac systems, but that is the way they are designed and the correct way for them to operate. Just like the high wall units, the actual t-stat is in the unit. The remotes are communicators but not controls.

From my experience in the mini-split business this was/is a common situation with cassettes and contractor knowledge about cassettes. You are going to love this system and it is going to make you very comfortable at a very modest operating cost. In our bedroom, with the high wall unit, we frequently run the fan only. Of course we have no humidity here, so...

Pay the man when you get an answer. The answer you are going to get is not cause to hold back. BTW, what brand is the equipment?

Thank you everyone.

Jackfre, I really appreciate your response. It's a Mitsubishi.