I have no heat and the A/C will not come on either... anyone know what this could be .

2001 trailblazer, computer climate control, the A/C light will flash 3 times then go out

 

Check your vacuum lines to your controls.... if they have fluid in them you have a falty vacuum switch on the transfer case. If that is the case then you should also check the transfer case fluid level, if it is over full then there is an issue with the seal between the transmission and the t-case...

 

I'll keep looking, but I can't seem to find any simple diagnostic charts for your problem. It seems that your heating and air conditioning system is controlled by the computer (PCM)
Any number of faulty sensor inputs could cause the malfunction

 

ok so it could be the engine temp sensor? I had an engine light on about a month ago and was told it could be the engine temp sensor or just needing a new t-stat, So I changed the t-stat and had the light turned off, never came back on. I had the rad flushed when the changed the t-stat, but the heater core was not flushed. now I have no heat, and noticed the a/c will not stay on when switch to the coldest level either... just wanted to give you the whole story.... thanks for your help.

could a blocked up heater core cause all of this? or maybe just the engine temp sensor

thanks

 

A faulty coolant temp sensor could definately cause the problem.

 

Hey I had the same problem with my '99 4.3 v6 4x4 about 2 mos. ago, then my mechanic flushed the heater core with a garden hose. Then 2 days ago I had it done again,but more thoroughly..he's puzzled; if it occurs again he will flush entire coolant system and lines too...

 

weird but heat is back today.... a/c will not come on but is that because it is cold outside? -8C. or should it come on no matter what? put it on the coldest setting and a/c light just flashes 3 times.