My company role in a project is centeral A/C subcontractor,Before one month and befor we going to supply the machines of the project, the owner ask us to replace units of indoor and outdoor machines with anthor brand which is a little expensive than what we agreed on the contract ,so when we asked him to pay some extra for this change he refused ,then after some days he sent to inform us that he will buy and supply the machines of the project by himself and the original value of machines according to project prices breakdown will be deducted from the project payments and he will pay us only for fixing charge.the value of the machines is more than 40% of the original value of the contract. should we have to ask for change claim acoording to this decreasing in the scope of work ? why ? and, how much?