APU and AC trouble

Correct, one would think so.
There is a phone #, email, parts diagrams etc. Contact them if this is the right company. I see heaters but no APU's.
Proheat — Proheat Product Support

 

Yes, I have seen many home mini splits that use that form of restriction. But all refrigerant systems that I am aware of, cautioning that I am not an AC tech, use a dryer in the system as moisture is a vary bad issue. Many dryers use a desiccant medium. Once this medium is saturated, the dryer must be replaced. This is why the general accepted "rule of thumb" is to replace the receiver dryer each time the system is opened.