# heater out



## D-rock (May 23, 2011)

clogged heater core


----------



## DannyT (Mar 23, 2011)

is it low on antifreeze? heater door motor burned out?


----------



## 95025 (Nov 14, 2010)

Sonoma Driver said:


> My heater went out in my 2002 GMC Sonoma. I replaced the radiator cap and the thermostat, as those are the most common solutions to this problem. Still no heat. Anyone know how to fix this without taking it in?


There are several things that are most likely to cause this.

First, is if it's low on anti-freeze. 

Second, having replaced the cap & thermostat, I assume you added more antifreeze. But it's possible that you didn't "burp" it, and that there is an air lock in the system.

Third, it is possible that the vacuum is messed up you're not moving baffles properly, meaning the warm air is being closed out.

Fourth, it's possible that you have a bad heater core. But when those clog, it happens slowly, not all at once.


----------



## Sonoma Driver (Jan 16, 2012)

Thanks for the replies, everyone. Now, pretend I don't know alot about cars (coz I don't, hehe) And answer me this:


It's good on antifreeze, refilled it after replacing thermostat.

Dr. Hicks, how do I burp it, I didn't know about that, but would like to try it

Also, what is the vacuum and how do I move the baffles?

Thank you and I await your reply...


----------



## 95025 (Nov 14, 2010)

Sonoma Driver said:


> Thanks for the replies, everyone. Now, pretend I don't know alot about cars (coz I don't, hehe) And answer me this:
> 
> 
> It's good on antifreeze, refilled it after replacing thermostat.
> ...


Before you had "no heat" did you have a gradual decrease in the amount of heat, or was it a sudden and complete change?


First of all, are you _sure_ you're good on antifreeze? More specifically, can you open the radiator or do you have to fill the overflow bottle? If it's the latter, sometimes it can take several fills.

Burping... First of all, this probably isn't the problem. Even so, some vehicles (like my old Chevy truck) had a little bleeder on top of the thermostat housing. I doubt that you have that. If you have a serious air lock in your system, one way is to loosen the upper radiator hose at the thermostat housing and "bleed" it. 

Vacuum leaks... Vacuum is usually what pulls those heating/AC baffles back and forth. It's possible that the baffle is stuck in the "cold" position, and there's not enough vacuum to pull it to hot. Does your cruise control work? If not, you likely have a vacuum leak. Also, when you change from defrost to floor heat, does the blowing air actually go where it is supposed to? If not, a vacuum leak is not allowing the baffles to be pulled back and forth.


Heater core... Were you experiencing less heat than normal, before it came to having no heat?


----------



## noquacks (Jun 5, 2010)

just a thought- try locating the return heater tubing and feel it without getting burned!! It should feel hot if the core is not clogged, with hot engine. If its cold with hot emngine, it is likely clogged preventing the hot fluid from circulating.


----------



## Billy_Bob (Sep 11, 2008)

You are best to get a factory service manual set of books (4 books to set - order from dealer). Then follow the troubleshooting instructions in that. And if replacing parts, follow the part replacement instructions in that.

However you can search google.com for the following words. Beware there is a LOT of misinformation on the internet...
2002 GMC Sonoma Blend Door Actuator


----------



## Sonoma Driver (Jan 16, 2012)

Dr. Hicks, to answer your questions, it SEEMED like the heat went out all at once, not gradually, although it's hard to say coz we've had cold days and warm days lately. Pretty sure antifreeze is good, though my father-in-law explain burping, so I'm gonna try that. Also gonna check the heater core hoses. Defrost/vent/floor heat goes where it's supposed to, which leads me to believe it's not a vacuum leak. This is what is so perplexing. Cruise control still works too. I will try all of your suggestions, thanks for the help.

Thanks noquacks and Billy_Bob too.


----------



## 95025 (Nov 14, 2010)

Sonoma Driver said:


> Dr. Hicks, to answer your questions, it SEEMED like the heat went out all at once, not gradually, although it's hard to say coz we've had cold days and warm days lately. Pretty sure antifreeze is good, though my father-in-law explain burping, so I'm gonna try that. Also gonna check the heater core hoses. Defrost/vent/floor heat goes where it's supposed to, which leads me to believe it's not a vacuum leak. This is what is so perplexing. Cruise control still works too. I will try all of your suggestions, thanks for the help.
> 
> Thanks noquacks and Billy_Bob too.


Have you checked out any "Tech Discussion Forums" for this particular vehicle? What Billy_Bob suggested about getting service manuals is good, but they're expensive. These discussion forums are free.

I've gotten EXCELLENT advice about every single car I've owned/repaired/restored from such forums. In fact, were it not for two particular Volvo forums, I would have long since built a fire under the vintage 240 I've been working on.


----------



## Sonoma Driver (Jan 16, 2012)

Thanks for all your help guys. We've found that the heater core needs flushed, so we're gonna do that. Also gonna flush the radiator, coz it's got the original orange manufacturer antifreeze in it from 10 years ago! So it's due!


----------



## Marty1Mc (Mar 19, 2011)

If you are going to change out that Dex-Cool, you may want to also pull the block plugs and drain it completely. Dex-Cool doesn't mix well with Glycol based coolants, so you want to get all of it out. I would flush the heater core separately from the engine and then pull the thermostat and flush the rest. You need to get it all out.


----------

