Redline Mechanical were the subcontractors hired by my general contractor as part of an insurance claim which required a new furnace due to water damage. Since we were also expanding the square footage of our house, we got them to install a central air unit outside as well as some duct work in the basement.
Despite having professional drawings from an HRAI certified engineer, they somehow managed to install the furnace completely wrong. They hooked the main supply riser to the return portion of the furnace and the main return riser to the supply portion. (For laymen: They attached the ducts that should be blowing air to the part of the furnace that sucks air in, and the ducts that should be sucking air in to the part of the furnace that blows air out. i.e. - our return air vents were blowing air, and our supply vents were sucking air in.) This is such a basic aspect of HVAC work that it defies logic how this could even happen.
That's not even the worst part. When confronted with this error their "solution" was not to fix it at the source. (Either rotate the furnace or otherwise fix the ducts as they come off the furnace.) Their idea was to open up a 20 square foot hole in my kitchen wall where the main supply/return ducts are and create some weird type of "X" duct so that they connected properly.
Now, I don't know if this was due to maliciousness (since it was probably the cheaper option) or ignorance but my HVAC engineer actually laughed out loud when I told him about their "solution." Apparently this "X" duct would have created a massive choke point for air coming and going from the furnace to the whole house. Ultimately they ended up coming back and fixing it the right way after they exhausted all other options but I was still left with a 20 foot hole in my kitchen wall.
Finally, I had some issues with the thermostat they installed in December and they never even responded to my e-mail. So much for customer service.