Well, I can't help much more now regards the relay without being there, relays are simple things and are either on or off and by nature of the beast either in a NO or NC state dependant if powered or not. If you have both contacts in the same state then I would say it's faulty.!

Regards the ATC then you would usually use a 5way valve for the open/close (Lock in Chinglish) so would only require one NO contact which you would turn on to open the drawbar.

For the REL (Taper clean) you would use a separate two-way valve with another set of contacts, this could be on a separate relay or on the same relay as the drawbar. Personally, I use a separate relay so I can control the Airblast independently from the drawbar. This allows me to only turn the air on when required so saving Air and power.

The Dust usually relates to the Air seal which protects the bearings while the spindle is running. Again this is operated with a 2-way valve but using separate NO contacts on the Spindle on/off relay.

But without seeing your ATC spindle manual then it may be different from how I describe above.?