Opinion by

The plaintiff submitted an offer with specifications for an engine and ventilating fan for use in the defendant’s coal mine. After some correspondence between the parties relating to a change in diameter of the fan, the defendant wired on April 24, 1912, “Please.hurry *140up fan as much, as possible.” This order was subsequent to a full and clear' description of the machine, and the work demanded of it by the defendant. . On May 13, 1912, the superintendent of the company wrote: “We finished installation of fan on May 5th, and started it on May 6th; we had it running in good shape. I made some tests of volume of air produced and found it short of the guarantee. I believe it would be advisable for you to come out here and go over the situation with me, so that you can see for yourself what the fan is doing.” It was found on examination that the fan was not properly installed, and when these defects were remedied, the defendant continued to use and operate the machinery in the place where, and for the purposes it was bought down to the time of the trial—■ one year and nine months later. The defense was that the change in the diameter of the fan from thirty-two to twenty-seven inches made it impossible to fulfill the guaranty. All facts in relation to these changes were well known by the defendant before the shipment by the plaintiff, and while the purchase price is stated to be $975, for which this action was instituted, the affidavit of defense admits, “The defendant would not accept the fan at the contract price, but would accept the same and pay the plaintiff at a reduction of one hundred dollars.” On the trial the defense was as to the whole consideration, on the theory that the machine did not do the work it was guaranteed to perform. Both parties were permitted to offer evidence as to whether or not the fan fulfilled the guarantee contained in the written contract. It appears that the fan was shipped two weeks after the plaintiff had notified the defendant of the propriety of changing its diameter, and in which the defendant acquiesced, and after it was set up and kept in continuous use for so long a time without any changes being made or demanded by the defendant, the court was clearly right in holding that the fan as set up, was the one the defendant accepted and used *141without objection. There was no suggestion of a rescission of the contract, or a return of the property. No testimony was offered from which a jury could fix with any degree of certainty any damages sustained by the defendant. The court stated, “If the machine did not do its work properly, the defendant would be permitted to set up any damages which it sustained by reason of the change, or a failure of the machine to be as guaranteed, but there is no averment in the pleadings, and there is no proof by which you could measure any damages.”

Under the rule laid down in Seigworth v. Leffel, 76 Pa. 476; Hime v. Kiehl, 154 Pa. 190; American Home Savings Bank v. Trust Co., 210 Pa. 320, it was proper to direct a verdict in favor of the plaintiff for the full amount of the plaintiff’s claim. The defendant is not in position to rescind the contract so as to escape its liability to pay for it. See Farquhar v. McAlevy, 142 Pa. 233; Spiegelberg v. Karr, 24 Pa. Superior Ct. 339. Where there has been substantial and bona fide performance of an entire contract, but failure in some particulars, not essential to the enjoyment of the part performed, there may be a recovery of the contract price subject to the right of defendant to set off damages resulting from the breach: Otis Elevator Co. v. Flanders Realty Co., 244 Pa. 186. To ascertain the amount of such damages there was no evidence adduced on this trial. Where a party discovers facts which warrant rescission of his contract, it is his duty to act promptly, and in case he elects to rescind to notify the other party without delay. What is a reasonable time or undue delay when the facts are undisputed, is a question of law to be determined by the court: Zeller v. Haupt, 41 Pa. Superior Ct. 647. The evidence admitted under objection did not affect the material facts involved, and after a full and fair trial on the merits we find no reversible error to justify a reversal of the judgment.

The judgment is affirmed.