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Old 24-08-2016, 09:32   #1
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grunert refer cylcing


I'm not sure this is the proper place for this question...

I have a Grunert ac475 Refer system that seems to work fine but...As we have 12V Frigoboat units we normally run those. The last time I used the 115v Grunert, it short cycled (on off on off). Runs good and cold but only few minutes at a time.

There is good cooling water flow and 119V at start relay. When it kicks off, I can hold the start relay down and it will run normally. Thermostats seem o.k.

I am guessing the run capacitor (top one or the bottom one?) has gotten weak, or maybe it is the relay not holding...getting weak. There was some pitting on the relay contacts that I cleaned of but no change.


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Old 24-08-2016, 16:44   #2
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Re: grunert refer cylcing

AC system cycling too often.

Your refrigeration unit will have a series of protective switches along with the thermostat to prevent system failures:
1. Low pressure switch to prevent system from reaching an extremely low vacuum. This condition is most often caused by low refrigerant volume.
2. High pressure switch is designed to stop compressor before high pressures above 200 psi may reach an explosive value. Overly high refrigerant pressure is caused by poor water cooling at condenser. Refrigerant Cooled down after passing through condenser on this unit should be less than 120 degrees F. Corrective action of both pressure switches would be to check refrigerant level at sight glass and feel temperature of refrigerant line leaving condenser.
3. Compressor thermo snap action switch mounted under a plastic cover on outside of compressor may be indicating excessive compressor temperature or it is just time to replace it.
4. Thermostat itself is the main normal control of compressor cycling. All thermostats on electrical compressors have built in temperature control and over load protection by way of a time/pressure control between compressor shutdown and the next start up. If these compressor short cycle off and on too quickly compressor will overheat and be damaged, not to mention waste energy. The thermostat can also cause short cycling if its sensing tube is incorrectly installed.

In testing to find what is causing this short cycling problem DO NOT BYPASS THE HIGH PRESSURE SWITCH AS DAMAGING EXPLOSION WILL HAPPEN If pressure goes high enough. Closing start relay is dangerous if high pressure is the problem.
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Old 25-08-2016, 07:07   #3
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Re: grunert refer cylcing

Thanks for the post Richard Kollman.

Your take for trouble shooting is excellent and I will defer to a refrigeration specialist. Any suggestions in the Titusville area (Space Coast)?

Thermostats probably not the problem as there are one for the refer and one for the freezer -- it would mean (and it is possible) they both gave it up at the same time.

Low press -- maybe, but we run cold immediately on start. I don't think I have low pressure switch

High pressure...The return cooled refrigerant I can touch it no problem. I don't think cooling is a problem, but the switch may be.

Compressor snap action switch? I found it under the cover. There are two (what appear to be) switches.

O.K. Time to call the experts. Are these switches the kind of parts a good tech would carry with him on the truck? I'd love to narrow it down to something so to have one service call.

You don't mention the possibility of the relay or capacitors?

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