Bad t-stat or something else?

[BryanH]

My USS-96 is cooling down to 30 degrees but it's running longer and more frequently than any of my previous machines have. The compressor is screaming hot to the touch.  It runs for 30 - 60 mins gets to about 30F and stops.  Then starts up again in about 15 mins (temp around 34F).

All coils on the evap show some frost and feel cold.  Both fans work when they should.  The T-stat on/off works, but there is no recognizable change in temp levels between setting 1 or 7.

So, I thought that the T-stat might be dead and causing the machine to run until overload, then shutdown until it cools enough for the overload to reset. So I watched the machine go through a cooling cycle.  When it shut-down, it just  stopped (didn't hear any kind of click).  I then checked for continuity across the overload switch (and then all combinations of the 4 contacts circled). They were all closed/on.  If the overload switch was triggered then I should have found at least one set of contacts being open (right?).

Could this still be a bad t-stat?  The t-stat on this machine is a pain to get to so I thought I'd check with you guys to see if you think it might be something else before I start digging it out.

[BrianB]

Sounds to me that the t-stat is on the way out. You have some control with it but not much. It sounds like the temp. cut in/cut out isn't working to well. It's supposed to determine when the compressor starts/stops from the completion of the cooling cycle to start of the next cycle, still a function of the t-stat and should be adjusted in 1/4 turn steps or less. Also, check your door seals and make sure you are getting good contact all around.

One more thing, make sure the intake through the condensor coils is free and clear of any obstructions. Let us know how things turn out!

[BryanH]

Fans and coils have all been sprayed and vacuumed...  not pristine but not bad.  I've got a couple questions about this thermostat.  Wondering if this coiling is standard on Cavaliers?  Seems to have some kind of grease stuffed into the center and then the whole thing is put inside a copper tube?  (I've asked the folks at SodaJerkWorks to send me a picture of the thermostat they have for Cav's - it's the only one they sell w/o a pciture)...

Next question: this was mounted on the right side of the evaporator.  Which means to get at it the entire evaporator has to be onbolted and shifted.  Any reason why I wouldn't be able to mount the tip of the new tstat on top of the evaporator (like they do with Vendos and Vendorlators)?

[BryanH]

Meant to add these pics with the last post....

[MoonDawg]

The evaporator did not need to be moved.  That copper sleeve was supposed to stay attatched to the wall of the evaporator and the cap tube is removed from it.

[BryanH]

Oh '>

So is the grey-brown stuff just crap and goo that has collected on the tube over the last 30 years?  Maybe that's what's keeping the t-stat from getting cold enough to shut-off?

[Creighton]

Bryan,
Here is a pic of my USS-64 T-stat. Mounted on the right side as well. 32 yrs of cr*p and dirt on this one too. It must have had some sort of oil to collect dirt this bad. Same coil.
Creighton

[BryanH]

Well looks like the t-stat is toast.  Set it for the warmest temp, let the compressor run for a couple minutes and then put the cap tube minus the copper sheath in a glass of ice water @ 32 degrees.  Kept running like it didn't care how cold it was. '>

[Creighton]

Bryan,
Let me know what you find out for a replacement. Suspect mine is toast as well.
Thanks!!
Creighton

[BryanH]

Creighton, from Steve @ sodajerkworks:

Quote

Yes, EP18 will work.  You will need to wrap the coil around a #1 phillips screw driver to get it to the coil to the size you need.  This has to be done on all t-stats, it’s not hard to do.

I'll be ordering mine (with a bunch of Ideal55 stuff) tonight.