T-stat problem???

[Slamking18]

Hi guys...  I finally got my CAV-876 pepsi machine going and I am starting to troubleshoot the cooling system.  Right now, I have the T-stat set in between the "off" position and "1" and it is dropping to temps of around 30-32 degrees before cutting off.  Does this sound right or do I need to replace my t-stat?  I tried taking it off to look at it, but the probe coming out of it is attached to the coil and I didnt want to take that all apart just yet.  If I do need to replace the t-stat, how to I find out what type to get and where do I get one that will work with my system?  Also, I noticed that the vend door seal is needing replaced and I am not sure where to find a replacement for my machine...   

Thanks in advance
Derek

[90grad]

It almost sounds like the probe (end of the stat line) isn't in the correct position.  If you need a new one, two of the sponsors of this site (The Soda Jerk Works and Funtronics) sell them.  They also sell the door seals.  The Soda Jerk Works has an on-line catalog.  Funtronics can be reached by phone (301-371-5246).

[johnieG]

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.....

[Slamking18]

Thanks for the replies... This is all very helpful information.  I talked to Eric? from Global Compressors yesterday about how my machine was running.  I wasn't sure how to tell what type of t-stat my machine had, but he explained to me that the contact type of t-stats have what looks like a spring at the end of its lead and the non-contact type is either just a straight lead, coiled a little or is bent around like a paperclip.  I looked at mine and it was just a straight lead (about 1/8" diameter) and it was bent around like a paperclip and clamped on to the lower portion of the coil.

I explained this to Eric and he said it sounds to be a non-contact type t-stat and that where it was mounted, was a bad place for those types of t-stats.  He told me to position the lead directly in the flow of air.  To position the lead in the air flow, I had to completely uncoil it and make it totally straight and about 2 inches of it is in the air flow now.  I did this after work yesterday and left the dial in between "off" and "1" to see how it changed.  I was checking the temps throught the evening and even this morning and every time I checked it, the compressor was running and it was at 35-38 degrees.  I don't know if it is cycling on/off or not but it seems odd that keep catching it while its running.  I was going to try to turn the dial up to about "2" and see what happened then tonight.

What do you guys think? Does this sound like its working fine?  Any help is appreciated...
I will take some pics tonight of my t-stat so you guys might be able to help me a bit more.

Thanks in advance
-Derek

[Slamking18]

Update:

Here are some pics of the t-stat in my machine so hopefully someone can tell me what I have.  Also, when I moved the lead directly in the air path, my coil was frozen solid when I came home and the temp was down to 65 degrees since there was no air movement..  Is this just a coincidence or what do you guys think?

[globalcompressors]

Looks like an air probe style...
It has been replaced at some point. When you straightened
the probe, could there have been a crack or break in the probe itself? if so,
the thermostat won't work either...or it simply could have gone bad.

Try replacing it, Funtronics, or myself sell this item. If the coil completely
froze over, solid, that's going to be the problem and I think a new one will
get you fixed up!

Eric

[johnieG]

MMMM frosty!  do you think from the bend in the middle of the probe wire, that this one could have been clamped to the side of the evaporator maybe?

[Slamking18]

That is where it was in the beginning...   I ended up rebending it back to look like a paperclip and I put it back in the clamp on the evaporator and I noticed that the clamp wasn't putting much pressure on the t-stat lead.  so I wedged a washer in between the clamp and the t-stat lead so it would have tighter contact to the evaporator.  It seems to be working better. Now I have the t-stat set to '3' and last night, when it was about 45 degrees, I started turning down the dial and it kicked off the compressor when I got to '2'.  So I am thinking my t-stat is working.  I turned it back up to '3' and this morning when i was leaving for work, it was 35 degrees and the compressor was not running.  I will know more tonight when I actually have a chance to monitor is cycle times.  I will keep you guys posted and thanks for the help.

[Creighton]

Great info on this thread thanks! One thing to add, have the machine full of product.
Creighton