They are saying air flow isn't the issue. Temp of air is the issue.

I'm suggesting blocking a pass vent to attempt and prove it is all part of the same ductwork and the warm air should show on the driver side...

How do you know there is not an airflow issue? The back of ones hand is only so sensitive.

Take another look at the pic with the heater core exposed. The part you see is the back side where air has already passed through the core and has been warmed. The heated air then goes into the "box" not knowing wether it will end up on the driver'* side or the passenger'* side. At this point, the heater core has done it'* job. It isn't until the air reaches the center flap that it is determined what air will go to what side.

Another interesting note that I missed previously:
The defroster ducts are a part of the main assembly. There is no real left or right defroster vent as it is only one thin opening with an interruption in the center where the solar sensor is. Otherwise, it'* wide open. The floor diverters are simple angled areas of the duct and the air also comes from the main assembly.

Looks like we've got quite a discussion going here I don't have anything new to report, just wanted to say thanks for all the thoughts and to respond to a couple of them.

I know that not being able to examine the situation first-hand leaves a lot of room for questioning, so maybe, if you can stand it, a bit of rambling from me might help.

I understand the thought about it possibly being a partial blockage in the heater core because I had the same thought earlier on. I also came to about the same conclusions. Unless the venting is separated, the hot air would mix and all air would become "warm", instead hot/cold right/left. Of course, being able to actually feel and observe the differences in temperatures of the air coming out of each side of the cabin gave me an advantage.

Once the radiator is warmed up, the air from the passenger side is VERY hot. The air from the driver side is VERY cold. Not warm... cold. There is no apparent mixing at all of the hot and cold air. If it was warm enough outside to tell if the a/c was on, I would know for sure, but if it'* not on, the air coming from the driver side vents is certainly cold enough to think that the a/c is on. To me anyhow. But one can never rule out any possibility, blocked core or whatever, until a cure for the problem is found. It'* just that the odds seem against it being the core.

I plan to measure the difference in temperature coming out of the vents with a thermometer this evening. Will post it tomorrow.

I agree that there hasn't been any testing to determine the strength of airflow and it'* certainly a reasonable point. I can't think of any place to readily get my hands on the equipment to measure it, so again, it falls back to being able to observe it first-hand. Being a Bonneville Club, I'm sure everyone here is as aware as I am of the vent locations on the driver side. IMHO, a very poor design. In the summer, blows all the cold air directly on the driver'* hands. I've learned this week that even with those two vents closed, it still leaks some air on the drivers hands. Mine were "frostbitten" this morning after driving only a few miles.

Certainly Randman is right about airflow being less, the further away from the fan and this slight difference can often be felt at each vent as he describes. Disregarding these slight differences, the airflow feels equal at each of the 4 dash vents. It also feels every bit as strong as it did before this problem came up. It'* only my opinion, but I feel confident in saying that the airflow does not seem to be hindered in any way. That seems to be true at any fan speed.

Closing the dash vents on one side to see if it forces the air on the other side to mix is a good idea. I didn't think of that this morning when I closed the driver side vents, but I will test it this evening. I'm not sure that I'll be able to tell if the passenger side air cools down, but I'll certainly try. I'll also reverse it and see if the cold air on the driver side warms up a bit. That might be easier to feel. I'll let you know.

Thank you for all the thoughts and posts you've sent. The info you've provided on tracking down vacuum leaks and on the vacuum control modules has been very enlightening. If Tim (98bonnie) doesn't find the problem before I have the time (and a warmer place) to attack it, I'll certainly keep you posted. This is a frustrating thing that needs an answer, for everyone.

You're a great bunch and I'm glad you're here.

Jim

alright guys! i've noticed that i'm FREEZING on the way to work! this is on my '91 park avenue with dual climate control. i'm guessing it'* a fairly similar system to the bonnevilles. i have the exact same problem... air flows great out of left and right vents, either defroster vents, or floor vents... no matter where it'* coming from, the driver'* side is "luke warm" at best...and the passenger side is HOT! the air mix doors are working properly from what i can tell from the outside of the heater box, if i move the doors, both sides get VERY COLD! move them back, back to luke warm on driver side, HOT on passenger side. i WILL find the problem! i just can't say when! i can't seem to locate an air flow diagram on how this system actually flows air :( I plan to spend all weekend on this in my heated garage if necessary. i've also got a parts car i can rip into... i should have it figured out by the end of the weekend! I will post any updates i find....

My problem is similar to this, but may not be related. I am getting hot air intermittingly, mostly cold though. I had it in the shop today and they said everything was fine with the thermostat, core and that they would have to take the dash off to check the electrical controls.

I am out of town and haven't had a chance to look into this, so I had them stop until I could check here for similar issues or help. Is there a 'blending door'?

Thanks for all of the discussion. It is helping me to better understand. First time to the forum.

Welcome!

Yeah, there is a blending door (air mix actuator) driven by a little electronic stepping motor used to determine how much air passes through the heater core before mixing with the air that passes through the evaporator. This is what moves when you call for more or less heat.

There are a couple or three posts referring to how to change it out, and how to "redneck" -rig the thing so you can get through the winter. One member figured out how to change it without removing the dash after I did mine the hard way

Not too easy to change.

Thanks!!!
I found your post and will look for the others.

going to yard to look at dash and rip one apart if i have too. since i started all this **** least i can do is try solve this problem . you guys r all great. thanks tim

I am anxious to hear the findings. This one is a good brain teaser.

Considering you have dual climate control, your problem is likely just the driver or passenger mix door. My boss has a 95 Riviera with this same problem.

Bonnevilles don't have the dual zone from 92-99.