I have a self-contained heating and air unit outside. In the winter the heat wouldn't work, but the air had been working on a newly installed system. I called a HVAC person and he said he bypassed something so that the heat would work. I called him this summer and he came back and switched the wires so that the air would work, but the heat won't work now. There is a grey wire hanging down from the wires coming out of the house and leading to the unit. I can see where he has spliced the brown wire together. What do I need to do to fix the unit so that both the heat and air will work without switching the wiring back and forth each season.

Sorry, but we need a model, brand and schematic to begin to help. I have seen literally hundreds of different self contained and roof top units over the years.

Also, did the technician tell you why he disconnected wires? There may be more to this, you may want to contact the company and find out why he did this before you start connecting wires.