Brad to run your plate at around -35 you would need to have a colder refrigerant so it would be on it's limits at around 2 psi. Here is an example of liquid Nitro (at the chemistry building)
Hi Smallwhale maybe you could call a different tech to check it out - sometimes two heads are better than one. You could have an intermittent fault which usually turn into permanent ones.
Maybe i should call my tech to change the temperature controller as its much cheaper to do it. Sadly.. my freezer playing up again :).. Left door shows -17.9 and right door shows -7.4 degree.. ...
Had this on a mercury unit with a Carel unit retro fitted to it. When it was fitted one of 4 available HP I/O's was used for a fault from a fan speed controller. Took a while to figure it out....



I've replaced the cap tube with 100" of a B-4 (should be well enough sized for R-22 system, 1/2 hp) and new dryer. The The only way I can get the suction up to 15 F is to get the condensing up to...
Delfield 2-door Reach-inCooler ...