the "equal" shoudl not only just be the product fromt he lsited manufacturer, also of equal quality. Let's say you designed arounnd the most efficient Trane chiller and lsited Carrier as equal. you only should accept an equally efficient Carrier chiller (and also equal maintenance etc.).
you should be free to allow a product from a not-listed manufacturer as long as it has the equal or better properties. (i.e. in case you didn't list york as equal chiller, but the model they suggest is better than your original ones, your client has an advantage of getting the York chiller).
I only can speak of Public Works project, and there I'm required to approve "equal or better" products. Obviously it is at my digression to way maintenance, efficiency etc. to determine what is equal or better. In case of trade-offs between efficiency and maintenance, you may talk to the owner / operator of the system.
in the end, you are serving the client and are required to find the best system for the client.