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Heater problems: passenger side blows cold driver side blows warm air

Resolved Question:

Heater problems, passenger side blows cold air, drivers side blows warm air. Dual control under passenger side dash not closing door inside heater box. Fuse? Where is it. 97 STS

Optional Information:
1997 Cadillac STS

Already Tried:
I've checked the fuses under the hood on the drivers side with a test light .All the ones that are powered up with the engine running have power on both sides. I don't have a owners manual so I don't know which one if any are for the heater controls. Everything else works as far as I know at this point. It just happen the last Friday as I was driving home from work, And don't you know the temperature was dropping down into the mid teens. Right when you really want to go outside and ---- with your car. I know that there are fuses on the back side of the rear seat if I go through the trunk but I didn't know if any of those control anything to do with the heater. I wouldn't think they would. But? The dual temp. control light Blue/red on the dash work I could take a test light and see if there is power being supplied to what looks like the motor that moves that rod back and forth that goes inside the heater box but when it Quit working the control on the dash was not lit and we don't usually touch it.

Submitted: 8 years ago.
Category: Cadillac
Expert:  autoservicetech replied 8 years ago.

Most new cars use a computer to control these doors, and there is no separate fuse to each one. Very common is an internal failure of the stepper motor gears inside the door actuator itself, and this requires replacement of the actuator.

You may try to remove the actuator you see that isn't moving, and then manually move the door yourself by turning the exposed shaft. Sometimes the door itself becomes jammed or broken, but it is not a common problem. If you can turn the door yourself, see if heat returns. If so, then it is definitely the actuator.

Customer: replied 8 years ago.
Ok now that it's a little warmer out tonight, I tried to close the door with the engine off by turning the shaft and was able to turn it to close the door. I started the engine and the actuator returned to it's origenal position. then I turned the tempture knob down in temp it turned back to where I had manualy turned it to, So now I know that actuator is working. Now My problem is again. I have warm air coming out the vents on the Drivres side of the car And cold air coming out the Passenger side vents. Both the floor vents and the mid dash vents. And it doesn't matter what I do with the Dual climent control buttons. Now what do I do. I'm going back out and see if I can try something else. Tomarrow It's going back down in the 20's. Please HELP. Thanks
Expert:  autoservicetech replied 8 years ago.

I'm not sure if this will apply....I don't have access to the service information here, but I can dig into it a little more at the shop tomorrow.

Many dual zone systems use a heater core that has two separate for either side of the car. Look under the hood, near the firewall and locate the heater hoses going into the cabin. If there is more than two, start the car and let it run until warm...make sure all the heater lines are hot. If not, it may be in a heater control valve, or blockage in the heater core itself.

If the problem happened all of a sudden, then I would look for a mechanical failure first before suspecting the heater core.

When you changed door position manually, did the temperature coming from the ducts change? IF this is a motor actuated door, you shouldn't have been able to move it without removing the actuator first. And there is more than one actuator in that casing. Are you sure you are looking at the right one?

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Customer: replied 8 years ago.

Now wait. Were not done. Let me check the heater core ? cores. First of all though, I did manage to reverse the condition when I turned down the temp. control to 60 and turn up the dual control to high heat for the passenger side. I got heat out of the passenger side and cold air out of the driver side. And to answer your question about the actuator. It did change temperature.from heat to cold out of the drivers side I know there's heat in the box. I can feel it coming out of the little seams.

Now to go back to your latter idea. I am wondering about your discription of the heater core. In the back of my mind in the very beginning when this started.

When the temperature here drops down in the teen.s 12 degrees Burrrrrrr. It takes a lot more heat to make you feel warm. I can tell in my heating bill. Maybe it had a lot more to do with the day we were having. But IT doesn't make sense that I can't get both sides to put out max. heat on high demand.

What about disconnecting the battery and resetting the computer? It's late tonight and I've got to go to work tomorrow. I'm going to go out and look at the possible of that dual heater core. maybe that side is restricted but it felt like a lot of heat was coming out of the Passenger side when I turned down the main temp. control and turned up the Pass side dual temp control..

Expert:  autoservicetech replied 8 years ago.
I'll do a little digging for you and wait to see what you find out. Try setting the controls manually selecting max heat, single zone, with the recirculation door closed. Let me know what happened...
Customer: replied 8 years ago.
OK I disconnected the Battery tonight and left it for about 10 mins. then I took a drive in the car to see what it felt like. When I got back, I took a temp reading of the outputs of both dr. & pass. Side and after ------- with the temp control and the dual temp control I was able to get, when I set it to 85 Degrees, I had between 84 & 90 Degrees coming out of both floor vents.Now it's 38 degrees here tonight. It's going back down into the tens tomarrow. I'm going to wait and see what happens tomarrow. I've got a feeling that when it gets that cold that there's not enought hot water going throught the heater core to keep up with the demand. I'm thinking with raw cold outside temp air, mixing with the now max output of the system that because of blockage that maybe ? the system might be compensating ??? OH!!! by the way, Sorry, I think tonight I found another set of pipes going into the heater box.I looked across from side to side for the hoses. there is two rubber hoses up on top on the passenger side and it looks like two steel pipes down below that come in from the drivers side of the engine that route around behind the back side of the engine over to the passenger side to the heater core. I looked to see if I could see hose clamps Accesable thinking that I need to back flush the heater core-s . That's not looking like an option from what I can see. I think I'd be better off takeing it to someone that claim they do that. Sorry if I sound questionable about service dealers.I've been in auto , marine, farm, golf cart , lawn mower service all my life. BUT a 97 Cadalic STS heater system is not my bag. I need help and I'm happy to find someone that is willing to talk to me .And willing to help someone that needs help with some of mine experince.
Expert:  autoservicetech replied 8 years ago.

OK, I did some digging on your system...let's start from the beginning. Here's what I want you to do....

First, disconnect the negative battery cable and let it sit for fifteen minutes. Then reconnect your battery, turn the key to the "on" position for 3 minutes...this lets the computer recalibrate the doors and perform its self diagnostic function.

Now, let's see if the computer sees a problem. You are going to put the computer in diagnostic mode by following this procedure:

Turn the ignition "on". Press the "off" and "passenger warmer" buttons at the same time, then press the "lo" fan speed button until you see "ACM?" displayed on the control display. Now press the "Hi" fan speed should now see "ACM Codes?" in the display. Press the "Hi" button again...any stored codes will be displayed. Let me know what numbers show up, if any.

This system uses a single heater core and two independent doors. The doors should work in unison in all modes EXCEPT "Dual zone" try MAX Heat in any position OTHER than Dual Zone and let me know how that works as well.

The two rubber hoses you saw are for the heater core, and the two aluminum lines are for the air conditioning system. Another possibility if you are getting heat from BOTH sides is a thermostat that is not closing all the way when it should. I personally use an infrared temperature gun to measure the temperature of the heater hoses going into and out of the heater core. This can tell me real quick if the coolant just isn't hot enough to begin with or if there is a restriction to flow in the heater core itself.

If you decide to take it to a shop, use the Shop Finder feature on this site to find a good one:

Let me know how you make way or the other. Take care...

Hang in there...