Works on AC but not on propane
AO airflow/draft is sufficient for removal of heat
AC Element and Propane transfer roughly the same heat energy to boil the ammonia coolant into a vapor
SO
Dirty Burner assembly
OR LP System Pressure is Low (S/B 11"WC --0.4psi. IF low the flame temp will be low and heat generated will not boil the ammonia in sufficient volume to absorb heat from food compartment)
**10"WC is 0.36 psi....can not visually tell difference between 11"WC and 10"WC. Need a manometer to measure system pressure...with at least 50% of appliances in service