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pincherman · 05-07-2022, 06:09 AM

I've done some thread and Google searching on this but have not found an answer.
I've got an ISL 8.9 in an '05 Newmar Dutch Star with a Spartan MountainMaster chassis.
While in idle if I turn on my dash air the engine stalls or more accurately just 'cuts out' as if its electrically being told to shut down. There's no warning lights when this happens.
As you can imagine I'm dreadfully afraid to see what happens if I engage my dash air while rolling down the road. Perhaps I should simply increase my RPM while idling and engage the dash a/c to see the result?
Just getting started on this issue and hoping someone out there has encountered the same.
Thanks for any help you can offer.
Dave

ArtJoyce · 05-07-2022, 06:55 AM

That is what I would do. Increase the rpms to maybe 1K. See what happens. I know on gas engines there is a idle increase when the AC is turned on. There use to an electric actuator on the carb for this rpm increase. I'm sure its built into the ECM now.

bentjm · 05-07-2022, 07:56 AM

I have a 2005 MADP. Same engine and chassis.

There is no way that your AC compressor could physically stall out your ISL - the compressor belt would slip/snap first.

You have an electric problem. It sounds Iike the AC circuit is "stealing" power from the ECM. I would start by looking at fuses and grounds.

Rob_M · 05-07-2022, 08:02 AM

It would smoke the belt before stalling that big cummins, even at idle. Has to be electrical somehow.

Fefanatic · 05-10-2022, 06:45 AM

The good thing is that the compressor is easy to get to for checking. Try to turn the clutch at the end of the compressor and see if it's locked up. If so then you are dealing with a bad compressor and a lot of debris in the ac system. Disconnect the plug on the high side line at the compressor and try to engage it again while running. It shouldn't engage the compressor as that is a pressure cut out switch. If the engine continues to run after the pressure switch is disconnected and ac engaged then you probably have a bad compressor. Leave it disconnected until you can get it serviced.

FWIW, revving the engine and engaging the compressor is a bad idea. If by chance the compressor is frozen and killing the engine at idle there will be a lot of smoke and belt damage if you rev it and engage the ac.

hypoxia · 05-10-2022, 07:57 AM

Quote:

Originally Posted by Fefanatic

The good thing is that the compressor is easy to get to for checking. Try to turn the clutch at the end of the compressor and see if it's locked up. If so then you are dealing with a bad compressor and a lot of debris in the ac system. Disconnect the plug on the high side line at the compressor and try to engage it again while running. It shouldn't engage the compressor as that is a pressure cut out switch. If the engine continues to run after the pressure switch is disconnected and ac engaged then you probably have a bad compressor. Leave it disconnected until you can get it serviced.

FWIW, revving the engine and engaging the compressor is a bad idea. If by chance the compressor is frozen and killing the engine at idle there will be a lot of smoke and belt damage if you rev it and engage the ac.

vito.a · 05-11-2022, 04:28 PM

On most Cummins diesel engines the A/C compressor has it's own dedicated belt separate from the serpentine belt that turns the water pump and alternator. This is because not all vehicles the engine goes into have A/C (like tractors and heavy equipment).

Diesel engines shut down differently than gas engines. Diesel engines usually have an electrical solenoid that shuts off the fuel. I'd try to find this solenoid in the fuel line to the injection pump. Put a test light on the wire and then have someone turn on the A/C and see if power is interrupted to the fuel solenoid.

Good luck!

Fefanatic · 05-11-2022, 05:21 PM

Quote:

Originally Posted by vito.a

On most Cummins diesel engines the A/C compressor has it's own dedicated belt separate from the serpentine belt that turns the water pump and alternator. This is because not all vehicles the engine goes into have A/C (like tractors and heavy equipment).

Diesel engines shut down differently than gas engines. Diesel engines usually have an electrical solenoid that shuts off the fuel. I'd try to find this solenoid in the fuel line to the injection pump. Put a test light on the wire and then have someone turn on the A/C and see if power is interrupted to the fuel solenoid.

Good luck!

His '05 should have a caps fuel system. There is no fuel shut off solenoid. The ecm operates the fuel valve through the stator on the fuel pump. To shut down it just stops opening and closing the fuel valve in time with injector firing. No solenoid and the ac circuit shouldn't have any effect on ecm controls of the engine.

pincherman · 05-12-2022, 06:32 AM

Responding to some of the posts thus far -
* If I start my engine with the A/C in the 'on' position, both the A/C and the engine run fine.
* However, I did have my A/C system purged and re-filled recently. Perhaps its just coincidental but as this issue was not there before maybe its got something to do with that A/C servicing event?
Thanks in advance to all that have responded to this point.

Ray,IN · 05-13-2022, 07:18 PM

I agree with replies 3&4 it must be electrical. Your cummins engine at low idle cannot be stopped by a locked compressor it would burn the belt apart. Also, your compressor is not locked according to your information update.

Fefanatic · 05-14-2022, 11:48 AM

Quote:

Originally Posted by pincherman

Responding to some of the posts thus far -
* If I start my engine with the A/C in the 'on' position, both the A/C and the engine run fine.
* However, I did have my A/C system purged and re-filled recently. Perhaps its just coincidental but as this issue was not there before maybe its got something to do with that A/C servicing event?
Thanks in advance to all that have responded to this point.

So, I'm not sure why you would have to purge and recharge the ac system if it is function fine. That being said refilling the ac system shouldn't have caused any issues unless it's overcharged with freon. Then it could build high head pressure and stop the compressor from turning.

So, to understand correctly if you start the engine with ac on it runs OK, but if you start the engine and then turn ac on it dies? Is that a correct assessment?

rvbiker45 · 05-14-2022, 02:27 PM

This is a silly thought, but, are you seeing no RPM's on the tach? Or, are you listening and feeling the stopping on the dash A/C? Maybe the A/C is stopping and the sudden stoppage makes it sound like the engine also quits.
Like I said, silly, but look under every rock.

pincherman · 05-15-2022, 03:02 AM

Quote:

Originally Posted by Fefanatic

So, I'm not sure why you would have to purge and recharge the ac system if it is function fine. That being said refilling the ac system shouldn't have caused any issues unless it's overcharged with freon. Then it could build high head pressure and stop the compressor from turning.

So, to understand correctly if you start the engine with ac on it runs OK, but if you start the engine and then turn ac on it dies? Is that a correct assessment?

I had the a/c recharged because the system was blowing tepid air and a big YES to your "correct assessment".

pincherman · 05-15-2022, 03:06 AM

Quote:

Originally Posted by rvbiker45

This is a silly thought, but, are you seeing no RPM's on the tach? Or, are you listening and feeling the stopping on the dash A/C? Maybe the A/C is stopping and the sudden stoppage makes it sound like the engine also quits.
Like I said, silly, but look under every rock.

No. The engine definitely shuts down and quickly I might add. That's big part of the reason I'm beginning to settle on this being an electrical issue.