Some of the new carrier RTU's now have freeze t/stat on the common side, that way you don't lock out for a freeze problem. Also 007 or tatle tale's don't work on safety side, you could try a small fuse maybe. I've had some luck that way, if you have the time put l/p and h/p and freeze in the control circuit with 007's on them and monitor the unit. Hopefully it will fail with you there, don't leave it that way or you could have bigger problems. Good luck.
"Nothing else can poison our culture, corrupt our society or ruin the character of our people like unearned money or unearned opportunity." -- James R. Cook
"Fooling around with alternating current is just a waste of time. Nobody will use it, ever." Thomas Edison, 1889.