Chris came today and observed the "fan not spinning" issue, and concluded there must be a problem with the brand-new low ambient control that he'd installed. So he took that offline for now, and is bringing a new one on Thursday.
Hopefully some testing was done to verify that the fan should have been running under the conditions the system was operating in.
If more government is the answer, then it's a really stupid question.
Chris came by again today, and said we have a 25-degree differential between supply and return, and that is too high. Apparently it's supposed to be around 20 or less. He thinks some additional airflow capacity will help this.
Low ir flow, so there is part of your freeze up problem.
His next suggestion is to add some additional ductwork to the master bedroom (the hot room on front of the house over the garage). He said although our ductwork is properly sized as a system, it's not distributing cooling well for where it's actually needed. Since we often end up freezing out the rest of the house to get the master comfortable, I think he is hoping that additional CFS in the master will:
If your duck system is properly sized, you wouldn't have a high temp delta. Unless there was an air flow restriction in it from blocked registers or duct liner coming loose.
Guessing they haven't checked static pressure of the duct system yet.
I'd agree with Mark, add the freeze protection thermostat and then work on getting the proper amount of air flow. You'll always need a "freeze stat" once you regularly set the thermostat below 70 degrees to eliminate nuisance freeze ups.