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Delfield Thermostat Probe Tests
Hey everybody!
I have a SSR2-S209 reach in fridge from Delfield which won’t cool.
I traced it down to a thermostat problem as the condenser fan isn’t running when it’s too hot which tells me it’s not even realizing it’s too hot.
SO!
What’s bad? The thermostat itself or the probe? That’s what I’m trying to figure out, does anyone have a magic number for ohms or some other way of testing these probes to see if they are still good?
Thank you.
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25 Replies
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Olivero, what you said confuses me. You said the condenser FAN isn’t running. What about the compressor?
As far as what probe it has, I can’t find anything on-line to reveal that. It could be an RTD, a thermistor or a thermocouple.
From what little I can find on the internet, a picture of the digital control hints at maybe a three-wire probe. If so, then that’s likely an RTD. Maybe one with a nominal rating of 100Ω at 32° and 110Ω at room temp. However, there are OTHER RTD probes out there at different nominal ratings.
MOST probes will either be good or entirely BAD. Have you done any resistance reading of it?
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Hey Ecto,
Yes, the condenser fan is not running and neither is the compressor, simply as if the thermostat is not telling it to run.
I think it’s a 3 wire type, either 3 or 2 but no I haven’t done ANY type of test since I didn’t know what to look for.
I left the unit plugged in and it intermittently doesen’t cool and then gets really hot, then if you tap the t-stat controller then it will start again a couple of times so I think it’s just a sticky relay on the t-stat board.
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Whats the evaporator fan doing? Staying on or cycling 3 min on and 3 min off?
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It is common for the control board relay for the compressor to die. I believe It’s only a 10 amp relay and the compressor start current is higher than that. I like to see a 20 amp ice cube auxiliary relay for the compressorin the line.
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The thermistors tend to either go full open or dead short on coolers. But the connection on the boards are also sometimes loose.
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As for the sensor test, this is what Delfield does;
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I didn’t show the clip for some reason. I should be 16,000 ohms plus or minus 1000 at 32 degrees F
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They recommend removing it and placing in ice water for several min.
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Okay, let me answer the first question.
The evaporator fan runs constantly, as long as the unit is plugged in, that fan is on. Always on every Delfield I got.
The condenser fan and compressor are not starting, but if I tap the t-stat then it will start shortly after, stay cold for an hour or 2 and then go back up to 70-80*F.
When I first went to check it, the comp was cold and the condenser fan was not on, that was a sure sign to me that the cooling wasn’t being initiated by the t-stat.
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That’s odd. They have a time cycle for low E on the newer ones. When the box is to set temp it only runs the evap fans 3 on and 3 off. If it’s running continuous it should mean there is a call for cooling. And it would indicate a bad control board.
Being these units are a spec grade, they can be set up a numerous number of options.
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I’m just asking because I don’t know: As a norm, does the display show SET temperature or ACTUAL temperature when the unit is on?
By your having to tap on it, sure sounds like the relay contacts in it are iffy. Are you able to do a voltage drop test across those contacts when the compressor is running?
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No problem.
It shows the ACTUAL temp, not the set one.
I could do that, I think.
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So…if it accurately displays ACTUAL temperature, then the probe has to be good and you’ll need a new temp controller.
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Yeah, it’s 2 probes in use.
1 is the display.
1 is the probe for the thermostat.
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Hmm? That’s wierd.
Again, I’ve been out of the loop for awhile on refrigeration, but I thought that Delfield used one probe for sensing space temp and the other for defrost termination. Seems I recall that even their refrigerators had a defrost cycle.
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They use a Danfoss controller. It actually has 4 inputs and and 3 or 4 outputs, depending on model. DO1 is rated at 16 amps where the other popular controller is only 10 amps. DO4 is a 8 amp relay The set-up is 4 pages long with a lot of variations.
This may help to understand it. https://www.galco.com/techdoc/dnfs/080g3216_ig.pdf
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One is the box temp, and the other is the evaporator temp. Used for defrost logic.
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I should also mention that the evaporator sensor is used to monitor ice build up. If it is off, it may not allow run to finish cycle defrost. It all depends on the controller set up.
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I finally found the full specs on the sensors. The 0 degree C is 16300. at 25 degrees C it’s 5000. They are color coded at both the plug and cable just back from the sensor with 1 or 2 blus stipes. 1 is box temp and 2 is the evaporator temp.
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