Higher CO reading

[rhigh]

Recently serviced my Posiden compressor, the air test came back with all passing marks except moisture. I replaced the PMV, install a new filter and now its pumping air that tests 7 ppm on my Oxcy-check tester.
It's an older compressor, but pumps to 2650 without issue.
Any thoughts on the higher CO readings?

 

[Doc Harry]

First question to answer is:
Is your CO meter properly calibrated and working properly?

 

[rhigh]

Yes, it routinely reads 0 on local shop fills