Not everyone is yet aware of organizational development and its benefits. But the awareness towards it is increasing. For making diagnosis, it's important to gather information for which your company should highlight the probable benefits it'll bring. Also, an orientation as to how your company will make a difference to the other's organisation before a diagnosis can help.
Also, making the employees aware of the whole program and showing them that they are a part of a bigger process can aid you with the work.
Hope this helps. Goodluck.
Organisational Diagnosis is a very new field and hence many people may be apprehensive about it at first. hence it is important to build a trust with the employees that the information they revel during this process will in no way hamper their work or position in the organisation.
Rapport building is also an important tool in getting the right information for an accurate organisational diagnosis.
building awareness about the benefits of organisational diagnosis in a positive line and marketing it well will help you in getting the employees to open up.
All the best for your future.