Summary: The technicians of Tetteris Heating &;;; Air Co. caused wide spread damage to the air conditioning and heating system while servicing the compressor outside. Tetteris Co refused to take responsibility for the damage, and they offered to fix it only if I pay them more to do so. On Monday, our A/C was working fine except the air temperature was not as cold as it should be. The HVAC tech from Tetteris Co worked on the outside compressor. They added two pounds of refrigerant and the temperature of the forced air became cold again. Then they opened up the electrical enclosure which is inside of the compressor cabinet, they disconnected several high voltage (220 Volt) connections, removed components. Then they replaced one of the capacitors, reassembled the wires and the components of the electrical enclosure. Then closed the compressor cabinet. One hour after the tech left, the A/C stopped working. The thermostat on the wall in the house was burned, we could smell the burn. And it was totally non-functional. Upon further discovery we saw that the wires and the components in the electrical enclosure in the compressor outside were burned and destroyed. Also, the circuit board in the furnace was burned and non-functional. The thermostat belongs to Potomac Electric Power CO, so PEPCO made a service call the next day (Tuesday). The PEPCO rep determined that the thermostat had burned internally due to improper high voltage having been applied. And the PEPCO rep diagnosed with his meter that the cause was that the high voltage (240 V) in the outside compressor was shorted to the low voltage (24 V) signal line which runs from the compressor to PEPCOs thermostat and to the circuit board in the furnace. On Wednesday, the Tetteris technicians returned and opened the outside compressor cabinet, then opened the electrical enclosure inside the cabinet and found the shorted wiring (as diagnosed by PEPCO) and burned components. Tetteris refused to accept responsibility for this damage. They have only offered to repair it for additional fees. Later this same day, The Don Hoffacker Company examined it, and stated that this kind of damage does not happen spontaneously. It only happens when someone makes a mistake to cause it to happen. It is understandable that a contractor, like Tetteris, can sometimes make a mistake. But, it is dishonest and bad business when that contractor refuses to take responsibility for their mistake.