i have a 99 sonoma, and have no heat, i have realized that the compressor is not engaging, also the thermostat is not reading, like its stuck open, temp only reaches maybe 120 then dropps back down?
Sounds like you have 2 problems. Worry about the compressor later. No heat; either out of engine coolant or failing or improper thermostat. And where you live may make a difference as far as ambient temperature is concerned. So what part of what country do you live?