An A/C system in your car that is blowing hot air instead of cold air is major inconvenience. Pinpointing the possible cause of the A/C malfunction requires the use of an A/C manifold gauge and some interpretation of the gauge readings. Some corrective action steps can be taken by the do-it-yourselfer, though other corrections may require the services of a professional auto air conditioning specialist.
Connect the low side hose (blue) to the low side port on the A/C unit.
Connect the high side hose (red) to the high side port on the A/C unit.