Botched AC service - Xpress Lube Revised

Below is a factual timeline. Long story short is that while well intentioned, Xpress Lube attempted repairs beyond their ability and my AC which arrived with somewhat cool air now blows none after three attempts. The Regional Manager refuses to do anything other than refund the service cost and the Shrader valve kit that the Store manager asked me to buy due to the AC showing up not working perfectly and the age of the car. Please read the letter and tell me what level of responsbility you would assing to Xpress Lube for repairs to my AC system, and how you would go about getting them cover my expenses.

*Minimum I would accept is to have them cover valve replacment that is now damaged and refund all previous charges.

17 July 10 AM
Wife takes 01 Ford Escape to Xpress lube for oil change. Tech suggests AC service and wife agrees. AC was not blowing very cold initially. No known AC service history.
17 July 4 PM
Wife notices Escape now blowing hot, returns to Xpress Lube. Tech states vacuum test passed first time, perhaps the Schrader valve allowed a leak. Recharges AC at no cost.
18 Jul 6 AM
Escape again not blowing cold air. I called Xpress Lube once they open. Manager states because vacuum test passed on the test unit both times that the Schrader valve was the only possible point of failure. Manager volunteers to perform service free of charge. At Managers direction I purchased Schrader components from Advanced Auto Parts after work and stop by.
18 Jul 3 PM
Arrive at Xpress Lube, Service begins.
18 Jul 3:30 PM
Manager still bending over car. He looks visibly frustrated and I approach him. He said that the valve in question was stuck and he did not have the right tools to get it out but that the tools he was using were allowing him to make slow progress.
18 Jul 3:45 PM
Manager seen using a hammer and a screwdriver in an attempted to get the valve out. I talked with another employee, who commented to me that he had no idea why the manager he was doing this, that he should have given me a refund, that we don’t do this type of repair here. I approach manager and ask him if I should take the car elsewhere and question his use of tools. He insists he can accomplish the repair. He talks on the phone presumable to his boss who presumably approves the expenditures. Sends employee to buy an easy-out tool.
18 Jul 4:30 PM
Valve is out, in small pieces. Stepping into the service bay and I looked into the valve where the valve stem had been removed and saw bits of scrapped and gouged / broken metal and pointed this out to the manager. I told him how I applauded him for his efforts but I feared that he was out of his area of expertise and equipment and asked that if this does not work will he cover my costs for going to another repair shop and getting the work done. He agrees. My wife arrives. I ask how much longer the repair will take and he says about an hour, that he must send his employee to get a second tool to install the valve. We exchange numbers and I leave.

18 Jul 5:30 PM
Repair complete Manager calls for pick up. Picked up 15 min later. AC appears to work very well. I ask how long this repair will last he states boldly ‘should work for years to come.’ He tells me if it doesn’t work he will cover the repair costs.
19 Jul 3 PM
AC again not working. On my way to work I stop by Xpress Lube and inform the manager. He tells me to take it to a shop. I ask if he is going to cover the repairs. He says he will.
19 Jul 11 PM
I submit online complaint to General Manager, seeking concurrence to cover repairs. I point out the use a hammer and a screw driver and the apparent damage to the valve port.
21 Jul 10 AM
General Manager calls, states due to age of car and already less than perfect condition of AC that the best he can offer is a refund of AC service and Schrader valve charges. Admits the Manager should not have performed reapirs.