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GM Tech (Cam)
GM Tech (Cam), Buick Technician
Category: Buick
Satisfied Customers: 29515
Experience:  GM Grand Master Technician 2007. 11 years experience.
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2003 buick regal custom: ac works fine..only blows..blows hot air

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i have a 2003 buick regal custom 3.8 engine that has heat issues. ac works fine at all levels, ie defrost, vent, floor. the heat however only blows hot air to vents, the floor and defrost are lukewarm. this one has me stumped.



The blend doors in the heater box under the dash are sticking, that's what's causing this.


Thanks for your question,



Customer: replied 7 years ago.
so how would have heat on vent but not defrost or floor?

The blend doors are not allowing coolant flow, just like the old time heater control valves that used to be under the hood, except more complicated. Part of the system is getting FULL coolant though it and part isn't.


Thanks again,



Customer: replied 7 years ago.
the defrost and floor have full air flow when they are selected, ac works great to floor and windshield. the air temp even changes to lukewarm as the heat control is turned to hot. so are you saying there are seperate blend doors for each level? and that only the vent one is working correctly? my understanding of the blend doors is that they mix warm and cold AIR not water. if that is the case then like i said the air flow is full volume to each level. please clearify

That's correct about the air, but the hot air wouldn't be there unless the coolant got there first to BLEND it all together. I don't want to argue sir, I've done hundreds of these, sorry you disagree.


Thanks again for your SUPPORT,



Customer: replied 7 years ago.
i am not arguing, just trying to understand. i only caped the air thing so that it stood out. sorry for any offense. so back to understanding then, if you are saying that the coolant to make the warm air is not there then how am i getting very hot air at mid level vent?
Customer: replied 7 years ago.
are you still interested in working with me on this problem or should i move on?
Customer: replied 7 years ago.
do you want to finish this question with me or do i need to somehow get another tech?
Hello, I will assist you from here. What is happening is as was indicated but I will often much more. Did you back flush the heater core? Dexcool is known for causing this sort of issue in teh heater cores. What I suggest you do first is take the heater lines off the core under the hood and use lots of fresh water and a garden hose to flush the core out, do this in both directions. A regular coolant flush will not usually clean the heater core enough. Try this and reply with your results.
Customer: replied 7 years ago.
hello thank you for working with me. i have flushed the entire cooling system. i have hot water on both the inlet and outlet hose of the heater core. i had already read about the dex cool issue. the dexcool was the consitency of paint when i got the car. i have flushed the entire system is stated new thermo, new rad cap, flushed about 50 gals of water thru system with cleaner. then put new antifreeze. the car no longer over heats and like i said there is hot to both sides of core. the describe the problem in full is that i have full ice cold ac to what ever level i choose. i have full hot air to mid level vent. i have only luke warm to floor or windshield. the last tech tried to tell that this was a stuck mix door, but i can understand how i would have hot to mid vent? i am not a novice mechanic, i am however not gm tech with years working on these models. so this is why i am seeking help. thanks
OK, thanks for the added details. Next does it do the same thing for both sides?
Customer: replied 7 years ago.
both sides of what? mid level vents?

Your car should have independent temp controls for the right and left sides so my question is if the issue happens on the vents and floor the same on both sides.

Customer: replied 7 years ago.
oh ok i will try it
Thank you.
Customer: replied 7 years ago.
the temo is the same on both sides. i was looking more intently at the heater core while it was warming up. let ask a few questions: is the lower line on the heater core the inlet? and the upper the outlet? if so how much should the difference temp be betwen those two?

THe heater inlet should be the lower hose. If working properly, there should be some change in the temp, how much I cannot say.

To talk this issue through, and consider the logic so we can get this figured out let me say this.

Because the issue happens on both sides and there are separate temp doors for each side, I think the issue is not electrical or a problem with the doors.

Let me ask you this, does the engine react proper operating temperature now? Have You changed the thermostat since the overheating issue?

Have you ever changed the cabin air filter?

Customer: replied 7 years ago.
yes i did change thermostat, i did not change cabin air but there seems to be no air resistence, plenty of air flow to all levels. with out putting a infra red thermostat on the heater hose i would say there is a about 50 degree or more difference in the two heater core hoses. whould that suggest a flow problem with with the heater core? if so could the core be air locked? if not then i guess restricted do to dexacool sludge could be a possiblity then. why hasnt gm recalled dexacool?

I cannot and will not comment on death-cool, oops I mean dexcool.

I do want you to try one thing just so we can say we tried it. Take the battery cables off for a minute and then put them back on. Lets force the module to do a relearn and see what happens.

Customer: replied 7 years ago.
ok i will try it, your such a good little corporate gm tech, lol
Customer: replied 7 years ago.
what about the question of if the heater core can become air locked?
Sorry I must have missed that. It is possible, but considering you have heat at both ends, I don;t think that is the issue. Also I an certain you have driven on the highway since all this happened and it did nothing to fix it?
Customer: replied 7 years ago.
i reset the computer and run the car to temp still no change. i have not ran it down the road much, it has however gone thru 5 or 6 heat cycles from cold to temp. back to the temp on the heater hoses, i am now clarifing and stating that the hose are not the same temp on both sides , that there is a significant difference in temp between the two by like 50 degrees the longer i let the heater run the outlet hose temp comes up alittle but they still are no close to equal. with your statments i am leaning toward air locked or gummed up with death-drool. what do you say?
I am also thinking the heater core. What I suggest is using a pressure washer in the heater core inlet and outlet. Take the lines off and route one to the other so you can drive to the car wash if needed. This may dislodge anything in there. Just make sure the other end is open.
Customer: replied 7 years ago.
other than pressure washing if that doesnt work, what other suggestions do you have without the dreaded heater core replacement?

IF we are 100% sure there is proper flow to the heater core, then I fear that is what is required.

I want to explore another area, that of the heater doors. I doubt it is the issue because both are the and chances are strongly against the doors failing at the same time, but given that the heater core is the worst case and checking the doors or even one will take a few minutes, I think wee need to eliminate that.

What I suggest is take the glove box out and find the actuator (picture below). Unplug and remove the actuator. Then with the engine running and hot, turn the shaft all teh way one way and then the other to check this. As I said, for the 15 mins this will take, I think we should check it.

Customer: replied 7 years ago.

no picture below came thru but i think i know where it is. i will try it.

ps if i wanted to ask you another question for a different car how would i go about it? you have been very helpful and patient. i would rather stick with you if i can. the question will be about a 95 buick lesabre cusXXXXX XXXXXmited with auto heat controls that the blower is not working. i have a long list of stuff i have already tried and diag-ed

Sorry, we try this again.

Object Number: 295333  Size: SH

To ask a new question for me, simply ask a new question and in the first line say FOR BLUEGORILLA ONLY!! and I will get it.

Customer: replied 7 years ago.
when are you online what hours?

I am online most every day 0700 to 2100 mst. I have my own computer in my toolbox and I check in often.

If you use the link below to my profile and ask the question, it have my system set up to send me an e-mail if a customer requests me.

GM Tech (Cam), Buick Technician
Category: Buick
Satisfied Customers: 29515
Experience: GM Grand Master Technician 2007. 11 years experience.
GM Tech (Cam) and other Buick Specialists are ready to help you
Customer: replied 7 years ago.
how confident are you in working on the electrical issue for the auto controlled hvac system on that 95?
If it is a blower issue I believe I can help you with that, but to be completely honest, if I feel that I cannot I will personally contact another expert that I know to assist in my place.
Customer: replied 7 years ago.
ok i will setup another question. i wont be able to try the heater core flush until tomorrow but i am gonna all this one finished
Customer: replied 7 years ago.
send me that direct link again so i can put it in my favorites then i will be able to get you next time i need help. thanks again
Customer: replied 7 years ago.
thanks again. today i am going to flush the heater core on the regal i will let you know the outcome of that later.

I look forward to the results.

Customer: replied 7 years ago.

I am very sorry, i forgot to accept your answer. please accept my apology. flushing the heater core did infact fix the problem. i am still having intermittent dexa-drool problems hopefully they will work themselves out.

thanks again