I wasn't trying to offend but in my experience it's not usual to come across an operator on the other side of the World from the US who is familiar with OSHA standards for something relatively obscure like CO exposure.
I did a brief trawl for any reports of odours in cabs (exhaust or otherwise) and all I came across was references to machines used in landfill applications, so there will be no magic bullet on this one.
The as-built machine is in the attachment. The key is the second line, 439-4922 Regional Option Arrangement. That is an option specific to Australia that opens up to reveal the Cab Arrangement which in turn opens up to show the Air Conditioner Gp specific to that machine. Now the possibilities have been narrowed down to one.
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Thanks for providing the hours. I was wondering if the machine had high hours that maybe higher levels of fumes might be a potential cause - but that's ruled that out.
Back to filters again - sorry.
There are two Part Number options for the circular fresh air filter. Can you ask the fitter which one is being used in the machine. I suspect I know what the answer will be but I would like him to confirm it.
Filter change interval. There is no recommended change interval in the manual. It's a "When Required" item because every job site will be different as regards dust and other contaminants. Can you ask what is the frequency in hours/weeks that the filters are changed.?
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Lastly, can someone stand behind the machine when the engine is being run at High Idle in neutral and see if they can smell exhaust being pushed out of the back of the engine compartment by the fan.