Write-Up: HVAC Assembly

Randall,
First off thanks for that diagram that will help a lot of people as there is always confusion as to the number of actuators and which one does what.

Actuators can be working perfectly but the blend doors internally can break and become detached from the actuator. When and if this happens it is a major job to correct. As you already know.
I don't know if that is your problem, but that would be the direction I would be looking as far as troubleshooting goes.
I would look in the FSM for where it shows the actual air flow. I remember seeing a diagram somewhere with arrows indicating air flow and how all the air moves about the plenum and control vanes. You need to then quietly wrap your head arouund this diagram that you just posted and the air flow diagram and try to figure out which one would be the most logical to attack first.
Then I would remove the actuator that I think is the one and manually rotate and feel the plastic shaft attached to the blend door and see if I could feel whether it has separated or broken internally somehow.
I haven't personally experienced this on a Riv but have on a Blazer that was near new, still under warranty, and the tech had to pull the whole dash out to gain access to the HVAC Air Box or Plenum, whichever you prefer, and replace a $10.00 part.
Poor bastard was paid flat-rate and they didn't give him squat for doing the job.

Here is the flow chart for what you describe. Hope it helps.....

Thanks for the posting the flow chart.
What I have also seen in the FSM somewhere was a more visual drawing of the HVAC box containing the Evaporator core, the Heater core, all the various mixing doors and deflector's with arrows indicating the air flow for different heating and cooling events.
I think all three of these, the one Randall posted above, the diagnostic flow chart above and the one I just mentioned would make the troubleshooting of the problem he is experiencing that much easier.

I have an illustration of the HVAC box and all of it's corresponding vents and ducts, but can't find one of what you are describing. I've seen it before too, just can't find it.....

This might be one of the figures you are talking about:



There is several more showing the different settings, in the '95 FSM they start on page 1C-9. I have followed the flow charts and even though the one you show above talks about differences in outlet temperatures when I was checking mine I had the pass. side control set to neutral so I would assume that with that not being adjusted up or down that all vent should be the same. The strange thing is I was getting almost the same readings on one of my Silver Arrows too?

I was able to verify that four of the five doors are moving on the '95, and it seems that after driving either one of them for ten to 20 minutes the temperature starts to equalize more than when sitting still. It does seem to be cooling fine so I put it all back together and am leaving it alone.

99Rivman wrote:

The system basically works as advertised in all modes, except, the conditioned air that comes out the vents on the driver’s side are not AS cold as the rest of the vents.
...the driver’s side vents put out 70 degrees, the passenger side vents put out 40 degrees, and the vents at the back of the console put out 55 degrees.

Check to see if you get similar temperature differentials when trying the heat... It sounds like the drivers' actuator might be frozen, but it also might just be "out of phase" with it's motor & location sensor. i.e., there may have been a gear that stripped/slipped a tooth or two, and thus the physical door is not where the computer thinks it is.

99Rivman wrote:

AND … I have a question for the experts out there …
This question pertains to my ’95:
I am having an issue with the HVAC, obviously, and in a Black car in 90 degree weather that is NOT a good thing!
The system basically works as advertised in all modes, except, the conditioned air that comes out the vents on the driver’s side are not AS cold as the rest of the vents.
Here is what I have checked so far, I physically looked at each actuator to be sure they are operating as they should, I checked the output temperature at all of the vents: the driver’s side vents put out 70 degrees, the passenger side vents put out 40 degrees, and the vents at the back of the console put out 55 degrees. All of this was checked with the ambient temperature at right around 80 degrees, engine idling, and a fan in front of the car. I have been through the SM trying to find any info that would give me a reason for the temperature differences and have found nothing.

My question here is, does anyone know what would cause the temperature differences between all of the vents when all of the actuators are working properly?

Any help would be great, thanks.

Did you ever figure out the problem with your Riv? Mine started doing the exact same thing last week.

I haven't had time to look into it any further for the last couple of months and since it does cool down after 15-20 minutes of driving it hasn't been a real big problem. When it gets back down to a reasonable temperature around here, in Nov or Dec maybe, I might check into it using the heater settings.
Sorry I can’t help.

99Rivman wrote:

Thought I’d put this out there just in case anyone else is having problems with their HVAC.
The first picture is of the driver’s side of the HVAC Module Assembly and the actuators that attach to that side, there are two more on the passenger side. The three on the driver’s side are the same part number and the two on the passenger side are the same also but they will not interchange from left to right. If you have problems with the air mix to either the A/C or Defrost or Heater these actuators are more than likely your problem.
The actuator has a 5 volt motor in it that turns gears that open and close the air mix doors. I had one that had gotten stuck on my first Silver Arrow and was able to free it up and it has been fine ever since. I was having problems on the new Silver Arrow, air wouldn’t go to the heater vents, and that was what I was looking into. After removing the left sound insulator I found out why! Some idiot had removed the #3 actuator in the picture and the air vent! Luckily they are the same for all years of the Riv so I was able to replace both parts with parts from my spare ’95.


The actuators are listed as follows:
1 Defrost Actuator
2 Mode Actuator
3 Air Mix Actuator

Hope someone finds this helpful.

99Rivman wrote:

I thought just for some clarification I would add the figure from the SM that actually shows all of the actuators…

Good post, very helpful. For clarification, can it be that the FSM drawing contradicts your initial photo ? I was trying to fix Mel's car today. with the AC ON, it's blowing hot air from the DS (not warm, slightly warmer than the pax side, but hot air) and cold air (AC) from the pax side. I want to remove the DS air mix door actuator but it looks like they are identified differently in your posts. I spent a good amount of time trying to remove the actuator you labeled #3 (#4 FSM). However I can't get to the back screw. I came to look back at the post to get a better view, but it looks like I should be trying to remove the one you labelled #2 (#5 FSM). Is this correct ?

I removed the one you labelled #2 (#5 FSM) and opened it up.

I consulted my 98 FSM, which labels the actuators the same way you did in your photo, both for name and number. However, I'm pretty sure 2 and 3 are reversed int he FSM. The temp up/down switch on the climate control ass'y rotates the actuator #2, which would make it the air mix door. The "mode" switch (floor/mid) rotates actuator #3, which would make it the MODE actuator.


<< fore aft>>



1 Defrost Actuator
2 Air Mix Actuator
3 Mode Actuator

Jason, how did you retrieve the HVAC malfunction codes (even though you didn't find any)?
I've had a problem for two years now where none of my actuators seem to work at all. I only get heat to the defrost/floor zones and can only control blower speed.

The hvac display isn't blinking. I used both an OBDII scan tool and DHP powrtuner.

Anyway, I took out the center actuator and found out the big gear was cracked.


My car has no heat on the driver's side. So I checked this actuator and that's what I found. It seems that there has been some retrofit parts for these actuators. The original part number lead me to another GM number and now to Dorman 604-111 and AC Delco 1572972. The best price I found for a new part was $72.58 from Amazon.com. With the extreme heat I see here in the desert southwest, I figured a used one will be cracked in no time. I'll pay the extra $50 for a new one, if I don't have to do this repair again! (Until the next actuator fails! God I hope not! )

VegasScott

Scott, thanks for posting the pic. I hope you have better luck with the next one!

99Rivman wrote:

This is the vent part that someone had removed!

Anybody know how to remove that piece he is refering too?

My console is still in the car, and I don't want to take it out if I don't have to.

Thanks,
VegasScott

VegasScott wrote:

Anyway, I took out the center actuator and found out the big gear was cracked.


My car has no heat on the driver's side. So I checked this actuator and that's what I found. It seems that there has been some retrofit parts for these actuators. The original part number lead me to another GM number and now to Dorman 604-111 and AC Delco 1572972. The best price I found for a new part was $72.58 from Amazon.com. With the extreme heat I see here in the desert southwest, I figured a used one will be cracked in no time. I'll pay the extra $50 for a new one, if I don't have to do this repair again! (Until the next actuator fails! God I hope not! )

VegasScott

What I did with this one I just rotated the biggest gear to a way that it will not touch the other gears. I figured that it only rotates half of its way, and the way I did it was connecting the actuator and tested it until it was well coordinated with the HVAC system, as the potentiometer (blue gear) is VERY sensitive. That way I saved my a$$ from a 100 dlls part

For the other part I think there is a screw right there in the square part, but to take it out you will need to pull it very hard and it will come off, don't worry about damaging the part as the plastic is very flexible

I glued my gear until I got a replacement from ed morad. At least the gear cracks and doesn't break a tooth off like the stupid hard to find gear in the cassette player.

I installed the new one that arrived yesterday and all is good with the HVAC now. It was interesting to note that the new AC Delco brand part has a plastic center section to the gear that connects to the blend door. If you look at the one that I pulled out, the center hub is metal and the outter gear is nylon. It is what failed. I'm hoping that since this looks to be one injection molded piece, that it won't fail as easily as the part ages in the desert heat here in Vegas. I'll predict that this one will fail many moons from now with a tooth issue and and not a cracked gear.

Thanks for all the info on this thread!

VegasScott

I did see one weird thing during the process. I now have a negative number being displayed for the external temperature. Any ideas?

VegasScott

That's not the only thing. The "Auto", and the "Off" button are on at the same time. Try disconnecting the battery. Maybe everything will reset.

Yeah, I saw that too. :

VegasScott

Terminal Dropped... Everything back to normal.

VegasScott

amazing....

what does Terminal Dropped mean?

deekster_caddy wrote:

what does Terminal Dropped mean?

I'm thinking battery terminal. let's see if I'm right