Hi Carlos, Im AL the owner of Big As Auto Repair.
Carlos, several things can cause no heat through the vents. Starting with the one that's mostly found. (1) Heater Core Plugged up. You see, when the heater core is restricted and the hot water is not flowing through the entire core it has little or no heat. (2) Thermostat stuck open. This can cause you to have very little heat because the water is not getting to operating temperature. (3) Low on coolant. If the water in the radiator get's low enough it also can cause little heat when sitting at an idle and get hotter while driving down the road. (4) Heater door not working properly. This is the lest likely but does happen. FIRST thing to check, "coolant level". SECOND thing to check, "coolant flow through the radiator" THIRD thing to check, "heater core plugged". Here's how to check the heater core. Drive your vehicle until its at operating temperature. Then grab one of the heater hoses going into the heater core under the hood. NOW grab the other heater hose coming out of the heater core. NOTE: If you can keep holding one, BUT must let go of the other one because its to hot to hold, then your heater core is plugged. You can try to flush the heater core but sometimes it doesn't help. But, lets try this first before replacing it. Take the heater hoses off the engine side NOT off the heater core itself. Plug one of the hoses up with something to keep the cleaner in the heater core, THEN, find a way to empty the core best done with shop air, then pour a radiator cleaner into the other hose until its full to the top, then plug it with something to keep the cleaner in the heater core. NOTE let it set over night then take the plugs out and flush out in both direction until the water coming out is clean. Sometimes this doesn't works, but its worth a try. Sometimes this cleans the heater core out and it starts leaking but, its worth a try. Carlos, hope this helps and please visit my auto-repair-website at: http://www.bigasautorepair.com/