My heat has been working off and on the past few weeks. I have manual hvac controls. It seems like when it's below 25-30 degrees it wont kick on, but when it's warmer it will (go figure). This morning I could feel just the tiniest trickle of hot air coming out of the defrost, but it wouldn't go full bore like usual. Does this sound like a vacuum leak or something else?

Also, sorry if this is in the wrong forum. I couldn't find one regarding hvac or anything really related.

 

sounds like ur coolant may be low. on my wifes 2000 suburban if the coolant is low itl go into 'limp' mode with the heater and take a while to heat up. idk

 

I dont know if yours is set up the same but if you think there may be a vacum problem look at this thred

https://blazerforum.com/forum/2nd-ge...-fender-66564/

But I would check your coolent levels in the rad and overflow and dont over look a air bubbe in the heatercore

 

Is the blower motor working? Usually the motor will crap out when its colder.