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Old 06-01-2019, 02:23 PM   #1
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Grunert Refrigeration unit

Have a Grunert Model 75 CDW compressor unit in the engine room with the 2 units ( Fridge and Freezer) in the galley. The units are in great shape but the compressor trips on start up. I've read some of the input here but no one discusses changing out the compressor only. i like the system in place now and it has worked well. I started having this problem a while ago and installed a start coil booster. However it has started again and I think the unit is just tired.
Is there any replacement for the Grunert Model 75CDW compressor that would allow me to do a straight change out. Also, we are in the middle of doing the Great Loop and really don't want to start changing out the entire system.
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Old 06-01-2019, 04:25 PM   #2
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Originally Posted by gerryhebear View Post
Have a Grunert Model 75 CDW compressor unit in the engine room with the 2 units ( Fridge and Freezer) in the galley. The units are in great shape but the compressor trips on start up. I've read some of the input here but no one discusses changing out the compressor only. i like the system in place now and it has worked well. I started having this problem a while ago and installed a start coil booster. However it has started again and I think the unit is just tired.
Is there any replacement for the Grunert Model 75CDW compressor that would allow me to do a straight change out. Also, we are in the middle of doing the Great Loop and really don't want to start changing out the entire system.
Seeking more information:
Both trip their breakers?
Under what circumstances do the breaker/breakers trip?
What size generator do you have?
Have you investigated a 'soft start'?
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Old 06-02-2019, 06:11 AM   #3
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Gather all the specifications you can about your" Grunert Model 75 CDW compressor unit ".

A refrigeration supply house , or digging on line, should reveal a number of similar capacity units.

These will vary in price but even the low priced units, A Techumsa will work for decades , a Copeland would be over kill.

The problem may be obtaining the Freon similar to what the system was built for , If it was F12 the auto supply should have recharge cans BUT some are a mix of propane and butane so be careful when flushing the system.
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Old 06-02-2019, 07:20 AM   #4
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Check the starting & running current on the compressor, check the resistance of the windings, also check the start gear - e.g. start/run capacitors, starting relay, if so equipped. A capacitor out of range can cause overcurrent conditions on startup. It could be that simple. Don't condemn the compressor without doing a thorough DX. If the steps outlined require more explanation, then you should call in an experienced refrigeration mechanic. Not some 20 yr old "tech" who'll recommend replacement because of a lack of troubleshooting knowledge.



Compressors are compressors. If it comes to replacement, the compressor will have nameplate that you can use to order a new compressor from a refrigerant supply house. Yes, the refrigerant may be R12. If the compressor must be replaced, it's imperative that it's completed by a qualified service provider who has access to the gear that's needed to complete that work. It requires that the system be pulled down, it will need to have nitrogen purge and a flow of nitrogen in the lines that are to be brazed. An oxycetelene torch is almost a must to be able to get the amount of focused heat needed to braze/sweat the joints.The dryer should be replaced, it may or may not have a suction dryer, probably does have a liquid dryer. Either way, compressor replacement always should include a dryer. The system should be pulled into a vacuum of 50 microns to confirm no leaks, and the vacuum broken with refrigerant to get the system re-charged.



Compressor replacement isn't terribly complicated for a qualified mechanic, but there's a lot of gear that's needed. It's not a DIY job even if you have the skills, you still need all that gear.



Recovery machine
Vacuum pump
Vacuum gauge electronic in microns

Nitrogen bottle, regulator
Oxygen/MAPP/Acetylene torch

Gauge set with vacuum port
Acid test kit (for compressor oil)
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Old 06-03-2019, 07:06 PM   #5
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Thanks for the help. We are in Deltaville, VA and there is a good boatyard here so we will have them do some testing for us.
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Old 06-04-2019, 10:01 AM   #6
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I think my previous response to OldDan1943 got lost somewhere in "Thread" heaven!
Both breakers trip when the unit is turned on. It runs for 2-4 seconds then trips. Generator is 13 KW. It trips either on shore power or generator. I am having an AC guy in Deltaville look at it on Thursday. Will check all the basics ( Start running currents, capacitor, resistance of the windings and the start relay before making a decision. I don't have the tools to do a changeout on this so might as well have a yard do the testing so we can get to a decision. A new Grunert equivalent ( AC475HA) is $5400 including new expansion valves + install which seems ridiculous and we might also consider going to a 12V unit. I like the cold plate units so will try to do what is needed to keep them. Will also look at other makes that would do the job. Maybe even a smaller compressor for each of the fridge and freezer units.
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Old 06-04-2019, 11:35 AM   #7
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Gerry, I hate when folks remember what I said and remember my name too. LOL

Can you start and run ONE unit without tripping? If so, turn it off and see it the other cold plate can start and run w/o tripping the breaker.

I would find it unusual that both compressors would crap out at the very same time.

Depending on what is discovered, either a "soft start" or a new compressor, keeping the box.
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Old 06-04-2019, 12:18 PM   #8
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There is only one compressor that runs both units so, given the problem is the compressor, I presume it would be normal that either unit coming on would trip the breaker.
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Old 06-04-2019, 01:01 PM   #9
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Slow down folks, step one should be to check the water flow.
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Old 06-04-2019, 01:28 PM   #10
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Water flow was the first thing I checked. Pump working fine and water flows immediately when unit is turned on.
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Old 06-04-2019, 02:18 PM   #11
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There is only one compressor that runs both units so, given the problem is the compressor, I presume it would be normal that either unit coming on would trip the breaker.
One compressor and one breaker? Seems reasonable.

The current draw is within specs.

Time to call the tech ...
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Old 06-04-2019, 05:37 PM   #12
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To the OP,

My boat also has a Grunert system, and like the OP I thought it was a good system and in some ways preferable to the alternative of having a 12v system always running.

My compressor also gave up the ghost (it developed a leak somewhere, and generally looked tired).

Instead of converting everything over to a new 12v system (Vitrifrigio, Dometic etc), instead I had the Grunert system rebuilt/reconditioned, and then recharged with the R12 gas. I found a tech here who knew the Grunert system like the back of his hand.

Cost was AUD 3.5k, and the system now works like a champion.

I am in Brisbane, Australia, and I reckon if I can find someone here who knows how to do that job you should have no trouble in the States finding someone knowledgeable and competent to do that work for you.

Good luck!

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