Kill Switch on Compressors

[jvtuna]

I have a 28 with KAMD42's and want to troll faster but the compressors come on just at the speed I want to go, can I kill the compressors to troll with no problems? If so, is it as simple as cutting into the wire and putting a switch in?

jvtuna

[Captain Spike]

I asked my service yard this exact question (they're Volvo agents). They asked Volvo who said not to do it but then I guess they would say that, they don't like people tinkering with their stuff. I'd like to hear from anyone who's tried it.

[Bullish]

I have the same problem as you. My compressors kick on at 1300rpms but I need to go 1500rpms to troll fast enough (7 knots). I have been complaining to Volvo for some time. Two different Volvo dealers have now suggested that we install a toggle switch on my dash to manually disengage the compressors while I'm trolling. I think that Volvo tells their dealers that this is a reasonable solution but they would not "publically" tell us.

What I have done this year, (which is a real pain in the butt), I pull the compressor fuse before I start trolling, which requires you to lift the engine hatch. This is not something I want to do on a consistent basis so I'm having the switch put in.

An important questions for me: how many hours a year do you guys troll with those compressors on? I seem to have worn out the clutch in one of my compressors because it runs all the time while trolling.

[Captain Spike]

My first season with the boat. I have KAMD43's and like you I need 1500 RPM to make 7.5 knots, I don't know how long the compressors will last running all the time and I don't really want to find out, I can't believe that manually shutting them down while trolling will present any problem so that's why I'm interested in any real experiences.

[Captain Spike]

I spoke again with Volvo technical and the guy sent me a photo copy of the electrical system workshop manual. This is what it says (word for word) about the supercharger.

"The engine speed (RPM) relay closes to ground via S1 and connects the supercharger. With an increase in engine speed S1 closes at 1700 rpm and breaks at 2400 rpm (KAMD) or 2600 (KAD) +/- 50 rom.

With a reduction in engine speed S1 closes 4.5 seconds +/- 2 seconds after the engine speed has gone below the set value 1700-2400 (KAMD) or 1700-2600 (KAD) and disconnects at 1400 rpm +/- 150 rpm.

Between 600-3100 rpm S1 closes if the "kick down" micro-switch opens and breaks + supply to G2"

So if I'm understanding it correctly the supercharger will come on at 1700 rpm unless I push the throttles all the way forward (kick down) in which case they will come on at any rpm. However if I throttled back from cruise to my 1500 rpm trolling speed the supercharger would stay on unless I first let the rpm drop below 1400 rpm to let the supercharger cut out.

The technical guy did also say that having them running all the time while trolling should not wear out the supercharger clutch but if they were constantly cutting in and out then that would cause premature wear to the clutch.

[Bullish]

This is very helpful. The clutch on mine probably burned out because of another problem I am having. The compressor continuously cycles for a few seconds just before the boat planes. This probably wore out the clutch.

Also, I paid close attention to the rpms last weekend when the compressor engages. My compressor engages exactly at 1300 rpms when I walk the throttles up slowly. According to your interpretaion of the manual, they should not engage under this method. If you test your boat in a similiar way, please let me know if you have the same results.

Thank you,
Jason

[Captain Spike]

According to the manual that the guy sent me you can adjust the speed at which the supercharger drops out but the speed at which it comes in is pre programmed into the electronic engine module.

It does however comment on possible causes of the supercharger cycling in and out in the "Troubleshooting" section. I'll quote it word for word.

"Oxidation or loose connections within the engine speed (RPM) sensor or the electronic module connectors. Cable breakage. Check and clean. The terminal pins should be smeared with contact grease"

It seems that this sensor's only job is to monitor engine speed and tell the supercharger when to come in and out.

[Captain Spike]

Another thought occurred to me. It's not inconceivable that US and European variants of the engine have differerent settings of the engine control module to dictate the engine speed at which the supercharger comes in. I live in England and spoke to Volvo UK who presumably gave me the information for the engines that they supply. Tigerlily was bought used in the US so the engines will be US specification. It may be worth you speaking with Volvo US and asking them for the info from the US version of the electrical manual.

[Bullish]

That's good information. Thank you. Did Volvo send you the complete electrical manual?

[Captain Spike]

I think it's the complete manual. Do you want me to scan it & email it to you?

[jvtuna]

Captain Spike,

Can you e-mail the manual as well? Also I think I undestand the workings of the compressor, but by cutting the wires and installing a kill switch means to me the current would just not get to the clutch and it would just not activate.
Would that be correct?

jvtuna

[Bullish]

Captain Spike-

That would be very helpful if you could scan the manual and email to me at [email protected]

Thanks very much.

Jason

[Captain Spike]

I'll do that when I get home tonight. Can you let me have your email JV?

As I understand it when you cut the cable the engine speed sensor still sends the signal telling the supercharger to engage the clutch but the current doesn't get through and the clutch remains disengaged so the supercharger doesn't run.

[jvtuna]

kill switch

Captain Spike my e-mail [email protected]


thanks

JV

[Captain Spike]

I've sent it now, I hope it's useful.