Never tried it on nasty carpet but it's not made for nasty carpet
I don't know about freeze/thaw.
4 oz in a 8-1 in-line type sprayer is all you need.
I mostly just poured it out into measuring cup rather than using pump, especially
when using 4 oz. 4 pumps equals 1/2 oz.
That's why I like to use a CRB after Prespray for HWE or VLM on residential. A vacuum misses a lot. What your vacuum misses the CRB digs out.
1 - Vacuum
2 - Prespray
3 - CRB with 1 or 2 trays
4 - Extract with TM for HWE or OP with cotton bonnets for VLM.
Me and Peter got the red bristle driver from New Again Carpet in Fort Wayne, Indiana (James) 260-210-3847.
I don't know the price now but I paid about $325 3-4 years ago. Just call James and tell him you want a red bristle driver for an Orbot.