Kohler 12.5kw Generator Question

[richard5933]

We had a great trip over Memorial Day weekend, but the temps were extremely hot (for Wisconsin) with daytime temps nearing 100 degrees. We ran the generator a few hours at the end of the day to allow us to run the two basement a/c units and get the coach cooled down for the evening. The rear a/c seemed to work well but the front a/c cycled the compressor off after only 3-4 minutes. It would cycle on again after a few minutes, only to repeat this over and over  but never run long enough to actually cool the front of the coach.

When we got home I confirmed that both a/c units run fine when plugged into shore power and cool nicely. No short cycling or other issues. Just to be sure, I'm going to pull the cover on he front basement unit to confirm that things are okay inside and that nothing is visibly wrong (coil clogged, fan motor binding, etc.)

My hunch was that the problem is with the generator. Generator is a Kohler 12.5 RCOP67

The power coming from the generator is steady at 117 volts 60 hz with no load. As the load increased with the first a/c unit the voltage dropped to about 112 volts, and with both running it dropped again to 108 volts. My thought is that the second a/c unit was having to work too hard to cool at the low voltage level and shut down. The manual lists low voltage as a possible cause of short compressor cycles.

Replacing the generator is the long-term goal. Either we'll put a brush-less 13 kw head on the existing Perkins engine, or replace both the engine and the generator with a new unit. Since the remote radiator and associated install of a full replacement would be difficult and too expensive right now, we'd probably opt for the generator head only. Either way, we'd like to push off replacement for now if possible.

For now, I'm trying to get information about how to remedy things for the short term. I've read elsewhere that I should set the engine RPM to provide for the proper voltage & 60hz operation at load (instead of at a no-load condition as it is currently set). This would mean a slight increase in the governor RPM speed. Seems like a simple solution which necessitates only turning a few screws. However, my experience teaches me that simple is not always best.

Anyone have experience with these older generator that can lend a bit of advice here? Is this a workable short-term solution? If so, should I aim for proper settings at a full-load situation or split the difference and have the unit run at 120v/60hz with half-load? My thought is to set it for half load so that on either end of the spectrum (no load or full load) I'll only be slightly out of spec. If I set this for proper setting at full load I'd be way off when at a no-load situation.

Thanks.

[dickandlois]

Richard, I Fixed up a 40 year old 3,500 watt generator that works real well, but it also has a load control issue. So I set the frequency at 62 at 122 volts to give it a little headroom and it handles 3000 plus with no real issues . The voltage drops to around 112 to 115 at 60.5 cycles. No problem as a backup when mother nature turns off the lights.

Wondering if you tried to run the front AC by it's self and how the generator handled it?  

Also, think your 12.5 KW might have 2 - 120 volt winding's and what the coil resistance is for each winding ?

A very small difference in the winding's could indicate an issue with one of the winding's. Does the Front AC units voltage change with time as things heat up - that could point to a thermal brake down in the winding feeding that circuit.

 Rich.

[kaypsmith]

Rich has very good points. But for answering your question about settings, I would go for half load, then test.

[abyrd]

I would expect that generators from your vintage have mechanical governors which are less responsive to speed changes than todays electronic/digital governors. It would be interested to know what the frequency was you were experiencing the problem.

I combination of low voltages and low frequency is definitely a problem for induction motors.

Jim

[richard5933]

I couldn't get a good handle on how the front a/c reacted when operated on the generator by itself. Seemed to do better, but to be honest by that time we were so hot and irritated that all we could think about was closing the bedroom door and retreating to the coolness that the rear a/c provided. My initial gut feeling is that the front unit hasn't aged quite as well as the rear for whatever reason. Possibly its location in the bay behind the wheel well caused it to catch more road spray? Who knows, but I'll hopefully find out if there is something going on when I open the cabinet. I'm also going to see what they used for a relay in the circuit that energizes the compressor. It's a mechanical relay/switch, so possibly it's part of the problem.

I'll be doing some more testing and inspecting over the next week, including opening the inspection doors to be certain that all connections are tight between the generator head and the control box, as well as in the manual transfer switch. Thought it would be good to eliminate the easy stuff first. Also going to open and inspect all components of the front a/c itself to eliminate obvious problems.

Once I have a better idea of the complete situation I'll figure out what to do, hopefully. Additional suggestions are welcome.

[manholt]

For the sake of, keep it simple...I'm with Kay!  I try to go with my first thought, when I over think a problem, I get into trouble!

[obedb]

Both units work when plugged into park (50 amp) power?  Perhaps I missed it, but does the front unit run properly on gen power when the rear unit is off? 

When running our Onan 7.5  diesel over the road for coach a/c, I close the rear of the coach off and run the front a/c only.  The genset is capable of running both units, but why burn the extra fuel necessary to "ice" the interior down? Park power easily cools the rear down at the end of the day.

The  gas genset on our first coach was tricky to keep running at heavy load from the gitgo. Bought a factory manual and a multimeter with frequency readout (from Radio Shack😊)  and tuned to the point that it would run both a/c s , the converter, microwave etc.

Good luck with it Richard.

[richard5933]

2 hours ago, obedb said:

Perhaps I missed it, but does the front unit run properly on gen power when the rear unit is off? 

Not totally sure on that. I'm going to run some tests to compare the current draw on both of the units. My guess is that the front unit is drawing more than the rear, and whether one or both of the units is running it's straining on the generator. My first steps will be to pull the cover on the basement unit and check the easy stuff...air flow over coil, fan motor lubrication (motor has oil cups), relay contacts, wire connections, etc, etc. Then I'm going to double check the generator to be sure that every connection is tight, that the brushes are in place and clean, and that the idle is set to provide proper voltage/hz at a medium load.

Right not the coach is in the shop to have the OTR a/c worked on. My Freon disappeared, and apparently it was due to the seals in my compressor drying out. These compressors were meant to be rebuilt and not replaced, which makes finding a replacement difficult. A seal kit is only $35, but they don't have anyone at the shop trained to rebuild a compressor or that has the needed tools. So, I'm having them pull the compressor to send to a shop in NJ that specializes in vintage buses. It will be another week or so till everything is worked out, but at least I'll avoid having to buy all new components to keep the OTR a/c going.

Once I get the bus back I'll start on the house a/c and generator issues.

[dickandlois]

The Motor has Oil cups, yep (motor has oil cups) That is what he posted. Hope they did not use 3 and 1 oil. 

Glad you found a shop that will tackle the Compressor !!

Rich.

Some CRC will clean the sludge out and then some TriFlow - smooth as silk...Old furnace motor trick.

[desertdeals69]

Years ago when Kohler was still in the RV gen business I was a dealer for them.  Watching my techs do adjustments, they set the cycles under load to 60 Hertz then it would go higher 1-3 cycles with no load.

[richard5933]

3 hours ago, DickandLois said:

The Motor has Oil cups, yep (motor has oil cups) That is what he posted. Hope they did not use 3 and 1 oil. 

Glad you found a shop that will tackle the Compressor !!

Rich.

Some CRC will clean the sludge out and then some TriFlow - smooth as silk...Old furnace motor trick.

I have not found any sign on 3-in-1 on the first basement a/c fan motor that I did this spring. Hoping that this one is the same. I must be getting old, because I still expect electric motors to have oil cups on each end. Still boggles my mind that they make things with no expectation that anyone will do maintenance in the future.

The OTR (over-the-road) compressor is being sent to US Coach in NJ. They are the go-to shop for all things old bus. Luke and Bill have been in the business for decades, have many OEM and NOS parts for coaches that are decades old, and still can do repairs that others only read about in history books. People with older bus conversions would be lost without them.

2 hours ago, desertdeals69 said:

Years ago when Kohler was still in the RV gen business I was a dealer for them.  Watching my techs do adjustments, they set the cycles under load to 60 Hertz then it would go higher 1-3 cycles with no load.

That is my plan - once the bus is back in my driveway I plan on setting the rpm on the governor just a tad higher than it is now so that it's proper under half load.

[richard5933]

UPDATE:

After doing lots of research and talking to the guy that services our home's a/c units, here's what I've done...

I opened both basement a/c units and did a visual inspection. Fan motors turned freely, and all wire connections were clean and tight. There is no visible damage or leaks anywhere. Used compressed air to blow the condensing coils - both were relatively clean and now even cleaner. The relay contacts were contained inside a plastic housing that didn't seem keen on being opened, so I left it alone. The interior units are really quite clean and all connections were tight.

All connections at the generator and at the transfer switch were checked. All were tight. No signs of overheating in sight.

Finally, I adjusted the governor on the generator to raise the voltage & hz just a tad. At no load it produces 120v @ 61hz. At moderate-to-full load it read 115-117 volts @ 60hz. Previous readings at load were just under 110 volts and 57-58 hz.

The a/c units both ran fine today. Both units blow cold and no short cycling yet. Fingers crossed. Of course, the outside temps are not that bad and only in the upper 70s. I'll be able to better test things in the coming days as the temps are expected to be in the 90s.

We're heading to Gillette next month and plan on dry camping three nights on the way, so we'll have a chance to test it out more thoroughly then as well.

If you think of something I've missed, please let me know.

[obedb]

Richard/ Years ago voltage was referred to as 110, then it became 115, and finally 120. We're compressors built to a different spec then and now?  Maybe you have been well within specs all along? 

Good to hear that things went well with your test.

[richard5933]

46 minutes ago, obedb said:

Richard/ Years ago voltage was referred to as 110, then it became 115, and finally 120. We're compressors built to a different spec then and now?  Maybe you have been well within specs all along? 

Good to hear that things went well with your test.

Well, that got me thinking...maybe I was chasing a problem that didn't really exist. I found this on Wikipedia:

AC systems started appearing in the US in the mid–1880s, using higher distribution voltage stepped down via transformers to the same 110 V customer utilization voltage that Edison used.   ...Nominal voltages gradually crept upward to 112 V and 115 V, or even 117 V. After WWII the standard voltage in the U.S. became 117 V, but many areas lagged behind even into the 1960s. In 1967 the nominal voltage rose to 120 V

My coach was built in 1974 and the conversion done at that time. So, I'm going to assume that by then 120v was the standard. Regardless, things seem to be working better with the increase in voltage/frequency.

Thanks for pointing this out though, as it was an interesting read.

[richard5933]

After having the problem of the front unit short cycling again, I searched out an HVAC tech that could help. Today the guy came out to look at the system. Just the kind of HVAC guy I needed too - he works on his own in his own company, and he has experience with both residential and commercial systems.

Seems that what Custom Coach did was use a commercial split system, just like you'd find cooling a large walk-in cooler, to cool the bus. Actually, two of them. The condensing units in the bays use heavy-duty 115v compressors, which he says are work horse compressors and should last years more.

The front system that was shutting down after a while was somewhat of a mystery. Some of the pressure/temps were spot on, others not so much. The one that worried him was actually the high pressure, and his suspicion was that the compressor was shutting down when the compressor reached it's internal high pressure/temp safety shut off point. The system was supposed to have r12 in it as refrigerant, but the pressures (especially the high pressure) were not correct. He tried to evacuate some of the refrigerant to see if there was too much. Didn't help. Then he evacuated the system, blew it out with nitrogen, evacuated again, changed the dryer/filter, and refilled with an r12 replacement that is supposed to be compatible with the oil in the system. His hunch was that there was a "non-compressible" in the system - either air or some other contaminant introduced by someone working on the system in the past. Presence of something like this would act to essentially downgrade the effectiveness of the condensing coil and raise the high pressure.

After the work he did, the system has been running with no problems so far. It's making cold (very cold) air and cycling on/off with the thermostat as it should.

While he was here, he checked the rear unit. It had bubbles in the sight glass so he topped off the refrigerant. Looks like we might have a very slight leak there, but not one that could be confirmed today.

We're going to run the systems on our trip over the next few weeks and see how things go. Good news is that the repair guy says that all the parts are still around, more than we'd need to totally rebuild the system if necessary. He was actually impressed with the quality of parts Custom Coach used to build the system.

I know that not many have systems similar to ours, but if nothing else perhaps it's interesting for others to read what it takes to keep these old rigs on the road. Maybe someone will also get an idea or inspiration from all this.

That's all for now.

[erniee]

you must have Cruisairs?

[richard5933]

1 hour ago, Erniee said:

you must have Cruisairs?

You might think so, but you'd be wrong. I thought that as well when first trying to get them worked on, which caused no end to the aggravation. It seems that half the battle is just figuring out what you've got and who is best to do the work.

When I looked closer I realized that these units have none of the things normally seen on a Cruisair unit - no nameplate, no 3-switch switch plate, and a totally different condensing unit. These units are running Copeland commercial compressors and the HVAC tech working on them today confirmed that they look identical to systems commonly seen in walk-in beer coolers or other medium-temp coolers. That's a good thing, really, as any parts needed are common commercial refrigeration off-the-shelf items.

The system was also put together in a manner which allows it to be serviced, very unlike the modern roof-top units that are often throw-a-way units once they break. There are also no circuit boards and no electronics. Everything is purely mechanical. A bit clunkier, perhaps, but certainly more reliable. After all, they've been working for 44+ years and still make cold air (temp at the blower was 50 degrees today with 85 degree outside temps, after getting the service completed.)