The dash a/c is a complicated affair because it is part Workhorse and part Fleetwood. Workhorse supplies the compressor and related parts but the dashboard controls, fans, ducting, etc. is supplied by Fleetwood. Either one could be the cause of your problem. If your Terra is under warranty, I would start from that end since you say it does not even appear to run. If not under warranty, then I would take it to an a/c shop and get a dignosis. If the a/c runs but the air does not cold, I would start from the Workhorse end and ask them to do the diagnosis and repair if it is a Workhorse warranteed part.
The compressor on my W22 just "self-destructed" one day when I turned it on, breaking the clutch and tearing up the drive belt. Workhorse replaced it under warranty without a question.
Former owner of 2004 American Tradition and several other RVs
Home is in the Ocala Nat'l Forest near Ocala, FL
Summers in Black Mountain, NC