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a/c help needed

Old 06-23-2019, 06:20 PM
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Default a/c help needed

So our cruiser is experiencing an issue with the front a/c while running of gen power. The compressor will not start up on gen power but will run on shore power fine. With a digital gauge, the ac voltage is 120 ish but like 68 or so hz on gen power where it is a perfect 120 and 60hz on shore power. Could the higher hz be causing the compressor to not start ?
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Old 06-23-2019, 09:36 PM
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Sounds like 2 A/C systems. Can the front A/C be started if the back A/C is off (and everything else off)?
Whats happens to the gen voltage when the front A/C tries to start? Does it dip waay down? Can you hear the generator struggling to keep up? Does the freq drop much? Do you have an A/C ammeter to measure the amp draw at startup?

It should run at 68 hz (apparently the rear A/C does) but that's going to make the compressor run faster than it should, causing more load on it than normal. There should be a speed/freq adjustment on the gen somewhere.

BTW, I used to have a 78 Carlson CVX-18. Cool little boat.

Last edited by zz28zz; 06-23-2019 at 09:43 PM.
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Old 06-24-2019, 08:07 AM
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Yes , two separate systems. The rear system runs fine of gen. The front system when it tries to kick on, draws about 40 amps and the compressor makes a rattling sound then does not start. This system has a soft start module installed so start amps should only be 20 and run is 10. It runs fine plugged into shore and sometimes will actually start and run on gen but most of the time will not start on gen power. A/C guy is saying that the compressor may be going out but odd that it usually runs fine on shore power, which is why I was thinking maybe it was the higher frequency.
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Old 06-24-2019, 08:48 AM
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not sure if the marine A/C systems have this or not but check to see if it has a starting capacitor. When the one on my home unit was going bad the compressor would make an awful noise on startup and it starting blowing breakers not long after that. Replaced the cap and it was back to being quiet.
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Old 06-24-2019, 01:18 PM
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No longer has a starting cap per say, it has a digital soft start module and a run cap. Again some times it runs fine on gen but always seems to run fine on shore power. Only difference there I can see is the difference in frequency.
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Old 06-24-2019, 01:53 PM
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the frequency could have an affect on the motor.....most motors that I'm familiar with have a 10% swing for voltage and a 5% swing for frequency...so if that was to hold true the frequency for your motor shouldn't go over 63Hz unless its built to handle it...
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Old 06-25-2019, 01:45 AM
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I thinking the shore power has a lot more current available and that's what is getting it going. When compressors get old they need more current to get them started. Too bad it's a soft start, I was going to recommend a "hard start kit". I'd try to get the gen freq adjusted before doing anything else, your rear A/C will thank you. It's possible the soft start circuity might be sensitive to freq, but I kinda doubt it. After all rear A/C starts OK.
Don't suppose the soft start circuitry can be easily swapped? Are the front and rear A/C's identical?
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Old 06-25-2019, 12:48 PM
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A few years ago my home AC was going through start capacitors.
I was told that it was because compressor was getting worn out and needed more power to get going.
I just replaced the capacitor with another original and it ran for another summer.
Next year was worse and I added a hard start kit that kept it running for one more summer.
Eventually the compressor just blew right up and died.
Oil into the fan, coils, and all over.
The hard start kit and everything got every bit of use out of it, but the compressor was just old, worn out, and drawing too much to get going.
Sounds like may be the same situation in your boat.
Shore power has enough current to not have an issue, but the draw is too great for the gen set.
Far from an expert here...just thought I would share what I was told and went through.
Good luck with it.
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