Newbie-Looking for HVAC Help Section - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 11-20-2009, 01:49 AM   #1
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Default Newbie-Looking for HVAC Help Section

I am new to the forum.

My '96 SE (mint, 105k miles, owned since new) is not making very warm heater air. I flushed the heater core, and it'* flowing freely, so I suspect a vacuum or electrical problem.

No flashing anything on the Electronic Climate Control panel-looks and operates as always (except not hot air, only warm. I don't think I am getting full air flow, either (though all blower speeds work by sound of it).

I understand there is an HVAC Help Section (mentioned in another post), but I am not sure where to find it? Appreciate if someone could point me to it...

Unfortunately I don't have a service manual for the car (It'* been so reliable I never needed one before!)

Thanks
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Old 11-20-2009, 02:15 AM   #2
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i'm just wondering how cool your motor runs? I've encountered a similar problem to this before and it was due to a thermostat being stuck open as it prevented the motor from reaching a temperature high enough to produce sufficient heat....just a thought.
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Old 11-20-2009, 08:08 AM   #3
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Try cleaning your EVAP core. https://www.gmforum.com/t278997/
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Old 11-20-2009, 09:34 AM   #4
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If your temp gauge on the dash is reading in the normal 180-200 area the most likely cause is the air mix actuator. Give that a quick search for how to find and diagnose it. If you have problems finding the info, holler up and we'll dig up some threads/info for you.
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Old 11-20-2009, 11:30 AM   #5
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Quote:
Originally Posted by incognegro View Post
i'm just wondering how cool your motor runs? I've encountered a similar problem to this before and it was due to a thermostat being stuck open as it prevented the motor from reaching a temperature high enough to produce sufficient heat....just a thought.
Yes, though the temp gauge reads where it has for the last couple of years (about 1/2 between the bottom and center, maybe 180deg) when I was getting great heat, I AM planning to replace the thermostat first. In fact, if the parts guy had not given me the wrong gasket with the thermostat (195 deg) I bought yesterday, I'd have the new one in already.

If I didn't seem to have reduced airflow in certain modes, I'd think the thermostat could be my only problem. I get LOTS of cold airflow until I select a warmer-than-outside temperature, when airflow seems to decrease markedly.

The car still gets great mileage (25 town/30 highway), and I would think if it were running "that" cool, the mileage would have fallen significantly (I got 28.5 in mixed driving on my last tank).

On the EVAP cleaning, I have not cleaned it, but using the A/C I get LOTS of airflow. Only when I select warm temps does airflow appear to decrease. I would imagine this means my evaporator core is not restricting airflow in heating-only mode?

I have a feeling I may have a mixing flap problem, like BillBoost is suggesting. I'll do some searches, and after I replace the thermostat, I will dig into that if the problem still exists (which I fear it will).


Thanks all,
Bob

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Old 11-20-2009, 11:59 AM   #6
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Bob, with that mileage, it'* not the T stat.
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Old 11-20-2009, 12:53 PM   #7
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Quote:
Originally Posted by BillBoost37 View Post
Bob, with that mileage, it'* not the T stat.
A few years back, I could get 32mpg on really long trips (all Interstate w/ no stops except for gas) at 70mph. I don't know what anyone else gets with these 3.8 engines, but there'* a reason I've kept mine for so long!

The Yokahama Avid Touring tires I put on in '02 gave me an extra 1.5mpg and are only half worn after 40,000mi, BTW. Tires can make a REAL difference.

Bob
My last Bonneville (same desert sand metallic) , a '66 w/ the 348cu, in would barely touch 20 on the highway, but it went 235k before rust got it.

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Old 11-22-2009, 08:19 PM   #8
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Update on my problem:

I changed the T-stat, and the temp gauge DOES read higher now, about 1 needle-width below the 200 deg mark now (vs 2 needle-widths before), but alas, no change in heater performance.

I removed and cleaned the grille behind the hood/in front of the windshield (heater air inlet), but really, it was pretty clean to begin with since the car was always garaged.

What I DID notice is that if the car'* interior is cool (55-65 deg), and I select any warmer temp up to 85 deg on the digital panel, I get luke-warm air (about 85/90 degrees) out of the heater.

If I select one "click" warmer, it goes from 85 deg to 90 deg and THEN I get REALLY hot air, which I measure at 165 degrees!!

Would I be right that if 90 deg is selected, the control panel calls for FULL HOT at the blend door, but at lower temperatures, the panel somehow measures the difference between the actual interior cabin air temp and the commanded (selected) temp, then uses a second temp sensor in the ductwork to determine what temperature air to set the air blending door at? I ask because I had a BMW that did that, and if the duct temp sensor, or the cabin temp sensor went bad, the heater never put out the right temperature air.

Unfortunately I don't have a detailed technical description of the HVAC system, but I did find the OEM GM Repair Manual for the car (2 large volumes) on Ebay and ordered it. Hopefully it will help, though you guys who have actually suffered such failures may still my best bet!

Any new suggestions?

I still need to remove the glove-box to see the air mix/blend flap move, but since it obviously it CAN produce really hot air when 90 deg is selected, it must be moving OK, making me ask about the actual temp sensors in the system, and what the control panel REALLY asks the blend door actuator to do.

Thanks,
Bob

Last edited by bobinyelm; 11-22-2009 at 08:22 PM.
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Old 11-22-2009, 08:24 PM   #9
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You can try this, not sure if it'* the problem, but worth a look. https://www.gmforum.com/t285293/
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Old 11-22-2009, 09:29 PM   #10
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Using a very soft long bristle paint brush, I was able to clean the sensor today through the openings and can see that the sensor wires and the face of the thermistor sensor are intact and very clean. It made no difference.

It'* possible that one (or if there'* another one in the system) has failed internally, of course.

Bob
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