Heater problems?

[WillMGK]

Ok, I think this is the correct section to post this in, so heres my problem. I have a 98 C1500 with a 4.3L in it. its a single cab. I just replaced the thermostat and the temperature sending unit i think, but both parts were on the upper rad hose thingy on the engine. I also put LEDS in my HVAC controls. The reason I'm telling you all this is because after I did both of these things my heater stopped working. I dont know if both of these things directly relate to that problem, But I thought it would be helpful to mention. Now, I live in Florida so I usually dony have to use my heater that often, but now as it is cold as ice outside, I start trying to use it in the mornings. Itll blow warm for a few minutes, and then blow ice cold again. My A/C works fine, but my heater does not work at all, Any ideas? Help please. Im freezing on my way to school in the mornings.

 

[4x4incountryboy]

blocked line, bad heater core? idk

 

[TylerZ281500]

so the blower works it just doesnt have heat coming in? how did you bleed your coolant passages when you filled her back up with coolant after thermostat replacement?
i was always taught to let the engine idle with the radiator cap off and the heat all the way to hot at full blast so your bleeding both you coolant system and your heater core. all my GM vehicles have had so much heat within 5 minutes of driving id have to completely turn it off. the one time i didnt the heat sucked.

 

[Swans.2000.3500]

This recently happened to me, check the lines that go into your heater core for blockage (They're located right on the firewall just down and to the right of the overflow tank) Or just change the heater core they are only $30 and take no more than 20 minutes to change