The newer 1/5 or less hp compressors with a 3 n 1 installed, will fail eventually, or as soon as a power surge hits it. I have seen both windings burn out. The 3n1 devices provide a much higher inrush current at start up than they where designed for. Also, that same inrush current may burn out the adaptive defrost board. Not a good thing for this to happen after servicing it as you are responsible for it's failure.
If you see an old fridg. with a compressor drawing more than 2.5 amp, you probably can use the 3n 1.

Thanks for the responses. Does this hold try on the new compressors if a RCO 810 is used? The RCO 810 is rated for 1/12 to 1/5 horsepower motors. My parts house always says it takes two weeks for the OEM parts to arrive.

I wasn’t saying you were wrong!! Nor was I trying to argue with you. [FONT='Times New Roman']I think you misunderstood the point I was making. I was in a round about way agreeing with you. [/FONT]

I was just saying I have used them in pinch lots of times with very few problems (no more problems than the correct relay). I only carry them just in case. I use the correct relay if at all possible. The fact that I have repaired many doesn’t mean it is ok to use it. I am just saying that I am not going to look a costumer in the eye and say you have to throw away all your food if I have a part that most likely put it back to work.

I wasn’t recommending using the 3-in-1 relays and I didn’t say you were wrong. I didn’t mean to imply that you were wrong.

I said (in so many words) that I have never heard/ didn’t know about the chance of the additive defrost problem and would look out for it because I believed that you wouldn’t mention it if it weren’t true.

I agree it probably don’t take much to burn out a 1/5 hp compressor.

Also I was not suggesting using a 3-in-1 if the correct relay will not start the compressor. I feel the same as you if I replace the relay with the correct relay and it doesn’t start I say the compressor is bad.

The last thing I want is problems with a repair I did, I don’t like return visits.

Thanks richappy and applianceman. I appreciate the help. I'm guessing that it does not matter if the smaller 3 n 1 is used. I noticed that a lot of techs just use the 1/3 to 1/4 rated 3 n 1 devices even on the newer compressors.

All compressors contain a Klyxon overload device that rapidly clicks open when the compressor current exceeds the rating of the compressor. This device is made with different current trip levels for each compressor. This device will open for a few minutes allowing the compressor windings to cool down. It is a very effective device and also provides over temperature protection.
A 3n1 cannot contain such a sprecific current trip level klyxon as it has to work over a relatively large current range. Instead, and due to the much larger inrush current it supplies, it contains a much slower current trip device that trips at a much higher current level and fails to provide an adequit cool down period.
In the event of a power surge, or power rapidly going off and on due to substation contactor chatter, the power rms value will exceed the compressor power ratings.
This device will work reliably in the "older" greater than 1/4 hp compressors as they have a stator with a larger and thicker iron core with a "softer" permeability characteristic. This prevents magnetic core saturation due to high inrush currents.
The newer 1/5 hp compressors have much less stator core cross section that can easily become saturated. This is done to dramatically increase efficiency. When a power surge happens, the reactance of the stator aproaches zero and the current is limited only by the copper wire resistance which is around 3- 4 ohms. This happens when the line voltage transients approach double voltage levels, which happens often enough. The peak power levels under these conditions could easily exceed 3000 watts. In the worst case, during substation contactor chatter, the power levels could reach 3000 watts RMS! I have witnessed compressor windings literally explode internally and short to the compressor housing.
Hope this explains everything.