A motion to open a judgment by confession shall be supported by affidavit in the manner provided by Rule 191 for summary judgments, and shall be accompanied by a verified answer which defendant proposes to file. If the motion and affidavit disclose a prima facie defense on the merits to the whole or a part of the plaintiff’s claim, the court shall set the motion for hearing. The plaintiff may file counteraffidavits. If, at the hearing upon the motion, it appears that the defendant has a defense on the merits to the whole or a part of the plaintiff’s claim and that he has been diligent in presenting his motion to open the judgment, the court shall sustain the motion either as to the whole of the judgment or as to any part thereof as to which a good defense has been shown, and the case shall thereafter proceed to trial upon the complaint, answer, and any further pleadings which are required or permitted. If an order is entered opening the judgment, defendant may assert any counterclaim, and plaintiff may amend his complaint so as to assert any other claims, including claims which have accrued subsequent to the entry of the original judgment. The issues of the case shall be tried by the court without a jury unless the defendant or the plaintiff demands a jury and pays the proper fee (if one is required by law) to the clerk at the time of the entry of the order opening the judgment. The original judgment stands as security, and all further proceedings thereon are stayed until the further order of the court, but if the defense is to a part only of the original judgment, the judgment stands as to the balance and enforcement may be had thereon. If a defendant files a motion supported by affidavit which does not disclose a defense to the merits but discloses a counterclaim against the plaintiff, and defendant has been diligent in presenting his motion, the trial court may permit the filing of the counterclaim and, to the extent justice requires, may stay proceedings on the judgment by confession until the counterclaim is disposed of.