OK, this is probably a dumn question, but here goes.
91 Prevost Liberty,
My issue now is the over the road bus air would not come on. At least I thought that was true. But today I happened to have the high idle on and tried the A/C and it came on. Now I am trying to remember if it was at regular idle when I tried it a couple of months ago and it did not come on.
Is it possible that the voltage was not high enough at regular idle or is there an interlock that prevents starting the system at regular idle ?

Anyone with any insight on this issue would be appreciated.
Thanks
Robert