Warranty call on upstairs gas system from 2020. Customer stated that the system isn’t cooling properly and it takes a very long time to cool the upstairs down. During my inspection I found the evaporator coil and refrigerant lines to be somewhat frozen. I informed the customer that I will turn the fan on and wait for it to thaw out. In the mean time I inspected the rest of the system to make sure there wasn’t any airflow restrictions. I also inspected the electrical wiring and found that the thermostat had the Y1 (stage 1) and Y2 (stage 2) terminals connected straight to the condenser outside which means the thermostat controls the compressor and tells it what stage to use based on demand. With that being said the variable speed furnace doesn’t recognize that the compressor has two stages so when the thermostat called for cool stage 2 the blower in the furnace stayed in stage 1 and would never kick on that second stage blower causing the system to freeze up eventually leading to the