06 Sierra SLT - Heat won't stay on!

[kda85]

First time to post here... so my apologies for giving too little or too much info...

 

Got a 2006 Sierra SLT Crew Cab Z71. Its just now getting cold enough for me to use the heat in the morning and for some reason it is acting crazy this year. No problems in the past. When my truck gets up to temperature I turned on the air and ran the digital temp number up 90 and nothing happened - air stayed cold. I turned the air off and then back on and it got hot immediately but 30-45 seconds later it returned to cold air. I repeated it a few times and it was hit or miss about 50/50 when the air would start blowing hot again (and it was hot - not warm so I don't think it has anything to do with the heater core). I have heard of the a/c being on and then going to hot but never the other way around. I do suspect that it wasn't actually going to a/c but to the ambient air outside the truck (40 degrees). It was like this on both the passenger and driver side - unlike when I hear of only one side acting crazy. Anybody ever experience this or know what is going on? How do I fix it? Can't go without heat - pretty soon I will have ice on my windshield that will need defrosting.

 

Thanks in advance for the help!

[servantsalesmen]

I think it's a problem with a temperature actuator. Lots of threads on here about it.