Hi @michaelt27032
Here's the [http://www.frankshospitalworkshop.com/equipment/documents/ventilators/service_manuals/Emerson%20CoughAssist%20-%20Service%20manual.pdf|service guide] that may help.
It shows how to replace the valve assembly and the valve actuator motor. Perhaps you could use the manual to check to see if there's a problem with either of them.
Here's the ifixit [guide|134156] that may also help.