[dennirob]

I have had the STS about 9 months now and having gone through summer/winter season, I think I may have blend door issues.

In the winter, the heat is working, but the car is still cold.
In the summer, the air is working, but the car is still hot.

I believe from the blend doors not closing completely and letting outside air into the cabin. Gets a little better on Recirculate, but still not blocking the outside air.

Where are the blend doors on a 98 STS? No codes.

Thanks
Robert D

 

[Submariner409]

The normal airflow configuration is to allow outside air into the car at all times except when the RECIRC function is set and, even then, the system will only allow minimum RECIRC until the system balances out. There are 6 or more ambient, cabin, duct and heat load sensors in the system. One glitch anywhere and things go wrong. Outside air is also heat controlled even with the system OFF. (A/C does not run, of course, but the system still tries to maintain the last temp settings.) Air enters the system, moves through the cabin, then into the trunk and out the two flapper vents in the lower inner rear fenderwell quarter panels.

I think there's a cabin air temp sensor in the pre-2000's, but the intake is up in the center of the dash area - at the center dash vents - instead of a little grille just left of the steering column. If that sensor (thermistor) is covered with dust then any temp balance compensation is slow.

Read your owner's manual for settings and basic operation, then go through your GM Service Manual for HVAC system diagnostic trees.

The doors and diverters are inside the HVAC stack itself - for replacement the entire dash, pad, and console front must be removed. The blend door motor controls are on the side of the HVAC stack in front of and beside the glove box - it needs to be removed. The rear console diverter door is down lower, near the passenger's left calf.

 

[Ranger]

Pull the DTC's. If you have a door problem, you should have a code for it. Be sure to post the code AND definition. We don't have them memorized.

 

[dennirob]

Ranger, No codes.

Sub, the cabin temp sensor is to the left of the steering column. I'll have to remove the glove box tomorrow.
Spent all day doing brakes on my F250 today.

Like I said, Heat/AC working properly, except for outside air coming in.

Am I even headed in the right direction with diagnosing the blend doors?
Or is it something else I need to look at to stop the outside air?

Thanks

 

[Submariner409]

To stop outside air from entering the car you use RECIRC. The little icon with a car and 180 degree turn arrow.

If the cabin air temp sensor ("aspirator") grille is to the left of the steering column, remove the grille with a paper clip hook and start the engine. Now blow out the tunnel with computer cleaner air. There's a thermistor at the tunnel entrance and further down, a board with computer muffin fan on it which fills with dust. This fan is also the occasional source of winter noise from the dash - buzzes and squeals. Several posts over the years in here and Tech Tips on how to replace the aspirator board or lube the fan.

Not sure just why you want to stop all outside air from entering - if the system is operating properly, the outside air has NO effect on cabin temperatures: The system can heat AND cool the air to uncomfortable levels with no intervention from you.............

 

[Ranger]

Does your ambient air temperature read the correct temperature?

 

[dennirob]

Sub, yes. I have been using Recirc to make it better, but still getting external air into the cabin. The reason I want to stop external air is because there is so much of it, the cabin does not get comfortably warm or cool, depending on the season. Winter, feet are freezing. Summer, almost at the point of sweating all the time.
Put your hand in front of the vents, feels great. Exact opposite on the feet. I dont have any pc canned air. Would an air compressor be too much?

Ranger, ambient air temp is correct on the dash.

Guys, I really appreciate you trying to help. Hopefully I am telling you everything .. I really am trying.

 

[MoistCabbage]

Sub, yes. I have been using Recirc to make it better, but still getting external air into the cabin. The reason I want to stop external air is because there is so much of it

The system (when working properly) doesn't just dump ambient air into the car at ambient temperature, it heats or cools it accordingly to provide the desired temperature. The problem isn't that "too much" ambient air is entering the car. If you're not getting any codes, first blow out the cabin air temp sensor with compressed air as submariner suggested. (personally I would use canned air as opposed to air from a compressor, only because it is completely clean and dry) also check that the sensors fan is running. With the car on, put your air up to the grille to the left of the steering wheel, you should hear a faint whirring sound.

If it isn't running, it might just have to be lubed with light machine oil. The fan/sensor is accessible by removing the cover on the drivers side of the dash (with the door open). Stick your finger through the rubber gromet and pull straight off. You'll see the fan/sensor is held on with one bolt (10 mm I think) remove it with a socket on an extension, carefully guide the sensor out of the opening in the side of the dash and unplug it. Hopefully that solves the problem and it's not an "in dash" sensor or blend door, they're a pain to get at.

 

[iametarq]

This is really strange. If your air blend doors were not working correctly you'd have codes, one for each side, but I don't recall what they are at the moment. My Seville gets them once in a while. Do you hear the doors trying to move when you cycle from a cool temp to a very hot temperature?

 

[Submariner409]

Yeah - his description of uneven air distribution points to mode door actuators - something's either hung up OR an actuator arm is disconnected............ now I don't think the RECIRC has anything to do with this problem............as posted, regardless of how much outside air enters the car, the system will totally control airflow, temperature, and humidity if the system is operating properly.

May I suggest a subscription to www.alldatadiy.com ?? This is the entire GM service manual plus tons more info - and it's instant gratification: you can have the manual in front of you 20 minutes from now. All diagrams and diagnostic trees, all DTC's, all recalls.......

 

[dennirob]

Thanks guys, I will try all of this in the morning. I finally got the brakes complete on the F250.
Will post tomorrow with the results.

 

[dennirob]

OK, the sensors fan is running. I do hear it. I blew out the sensor, which really was not that dirty. But I guess any dirt is bad.
Unfortunatey, my wife has driver the car every day and I have not had a chance to check it.
I would still like to remove the sensor fan and clean/oil it.

Reading back thru this post, sub mentioned the rear diverter. The rear works great. I also still need to pull the glove box out and see what I have there too.

 

[MoistCabbage]

When you say the rear works great, do you mean the heat is very warm and the A/C is nice and cold? Also, in your first post you say "In the winter, the heat is working, but the car is still cold.
In the summer, the air is working, but the car is still hot.". What temperature do you set the system to in summer/winter?

 

[dennirob]

Thanks everyone ... I blew out the sensor and oiled the fan and all is well.

 

[iametarq]

Thanks everyone ... I blew out the sensor and oiled the fan and all is well.

Happy endings are great.

 

[V8freak]

i got a quick question, im looking at a 98 sts 150,000km's. they want 1500 i offered 1000, anyways. My question, car has no heat, i drove it too my shop today and also noticed that with heater on full speed and temp and everything imbetween that the defrost will switch too the vents back and forth at the same time fan speed seems too change slightly. Any thoughts? i dont want too be chasing ghosts if i buy this thing

im thinking mode control door? possibly low vacuum?

 

[MoistCabbage]

It's all electric motors, no vacuum.

Go to the top of the Seville/Eldorado page, and read the "sticky" thread on how to pull codes. List any codes you may find, AND THEIR DEFINITIONS, here (there's a link within the sticky with definitions).

BTW, :welcome: