There are basically two types of thermostats used in soda machines,type "A" senses the air temperature & generally has a short coiled capillary tube sensing tip which is in the air stream of the evaporator fan. or just to the side but does NOT contact any metal at its tip, this type may also have a sensing "bulb" of a larger diameter tube with a rounded end. next is type "B" that is physically attatched to & senses the temperature of the evaporator core itself & & usually has a longer sensing capillary tube that clamps to the metal of the evaprator, or it may be inserted into a protective tube that also is in metal to metal contact with the evaporator core.
Air contact type "A" in this example, will typically have a fixed cut in ( turns on the compressor) temp of about 40-45 degrees F. & an adjustable range of 10 degrees of "cut out" ( turns the compressor off) say as low as 28 to 30 degrees F. up to the fixed cut in temp. in other words it will maintain the air temp between 28 to 40/45 degrees in this example.
the type "B" metal contact type will have a much lower operating range, why? because the temp of the metal of the evaporator will be around 10-20 degrees colder than the air it is chilling due to termal transfer rates betwen the air & the metal coils. say a cut out range of 28 degrees & a cut in range starting at 5-10 degrees F. so in this example ( with a temp difference of say 20 degrees between the metal to air 20+28=48 degrees cut in AIR temp.
there are many different tempurature cut in vs cut out ranges depending on your application available, but pay attention to were your original thermostats sensing tip is mounted ( in the free-air, or clamped/in physical contact to the metal of the evaporator.
if you use the wrong type ( say a type "B" ) in the free-air, guess what will happen? yep! frozen sodas! or if you use a type "A" installed to the metal evaporator the compressor will shut off too soon & you'll have tempid soda at best. so now, off to the races.....
