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rooftop A/C / Heater combo blowing air not cold

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The unit I refer to in the title is 2 years old. It was blowing cold air last week and now does the same thing except the air is now not cold. on the breaker panel all breakers are ok. Are there breakers/ fuses on or sometimes by the unit itself? What recommendations should I follow in the way of a priority checklist? The thermostat settings are the same as when it last worked.