Understanding the HVAC system

[JPul]

I am having an issue with my HVAC system and am trying to understand what is going on.



With AC on, the driver's side blows significantly cooler than the passenger side. This suggests that the refrigerant side of the system is fine but there is a potential problem in the mixing/distibution box. I would have thought that the temperature blend door would be common side to side so this difference is hard to understand. I have an ST and am wondering if the same basic system is used for all packages including the dual climate control and the ST just ties them togather but there could be an individual side problem.



Then, of course, what is the actual problem and how to fix?



As always, I appreciate any assistance in solving this issue.



Regards, John

 

[JApol]

The way the system works is that when the charge gets low the drivers side gets the cooling and the passenger side get little to none. The freon is a little low in the system. Bring back up to spec and you should have cold air on both sides.

 

[sag2]

JApol is correct. If you took the HVAC box apart and studied the air flow over the evaporator as well as the freon path through it, you would understand why it gets warmer on the driver side when the charge gets low.

 

[HHhuntitall]

Wait a second, I thought the 3rd gens had two blend doors, and if one broke, it would only let cold air to the driver side? Where is the article in the TDR that was done a few months back? Was that Mr. Donnelly or Mr. Patton? You might need to check that article out and research it before you start tearing your dash apart..... I can't find it at the moment.....

 

[sag2]

That's what were saying, no need to pull the dash for most complaints of warmer air from the passenger side. Check the charge first before digging deeper into the dash.

And to answer your question, on a single temp system there is only one blend air door.

 

[JPul]

Thanks guys. I think I understand.



The truck is 5 years old so I can see that its certainly possible for it to be a little low on refrigerant.



Regards, John

 

[Bob4x4]

Wait a second, I thought the 3rd gens had two blend doors, and if one broke, it would only let cold air to the driver side? Where is the article in the TDR that was done a few months back? Was that Mr. Donnelly or Mr. Patton? You might need to check that article out and research it before you start tearing your dash apart..... I can't find it at the moment.....

He has an ST I doubt you will find one equipped with dual Zone

 

[HHhuntitall]

Well, I thought the article I read said they had the dual doors, even when they didn't have the dual controls..... I've been looking for that article, I think it must be in issue 65 or 67, as they're the two missing at the moment... . and the reason I focused on it is mine is doing the same thing... ... certainly not saying you don't know what you do... . I'm just wanting a little clarification... .

 

[sag2]

You had me second guessing myself so I looked at the FSM and it only has one.

 

[HHhuntitall]

Ok. Guess that answers that... . now, what the heck was I reading?!? Hmmm,

 

[RVTRKN]

I am having an issue with my HVAC system and am trying to understand what is going on.



With AC on, the driver's side blows significantly cooler than the passenger side. This suggests that the refrigerant side of the system is fine but there is a potential problem in the mixing/distibution box. I would have thought that the temperature blend door would be common side to side so this difference is hard to understand. I have an ST and am wondering if the same basic system is used for all packages including the dual climate control and the ST just ties them togather but there could be an individual side problem.



Then, of course, what is the actual problem and how to fix?



As always, I appreciate any assistance in solving this issue.



Regards, John

Has your blend door been repaired in the past and if not, it is a good chance it is the blend door. I complained about this very problem when my 04. 5 was under warranty and was told its normal. Until I got past the service writer (not my service writer any more) and they found a faulty condensor and replaced it. But my wife still complained about her air being warmer, and as a good husband, I didn't take her serious. The blend or vent door got so bad that you could start to smell Diesel exhaust when behind a truck even though the AC recirculation was on. I had to pay for the repair and was told it was in that condition for a long time. You might want to have it done anyway to replace it to the newer style door and see if its makes a difference. It will fail sooner or later.

 

[JPul]

RVTRKN,



I have not had any problems to this point. The truck only has 20K miles on it. The thing is, the air coming out of my side is what one would expect with the A/C on so I'm trying to figure out how a buggered blend door would still give me cold air, but the passenger's side only gets moderately cool air. thats what got me thinking about a dual system that is just tied together for the ST.



I suspect that those that have already personally replaced the faulty blend door would have a real good understanding of how this door functions and if it would be possible if one half could be OK while the other half is buggered.



I recall reading something about an A/C issue in one of the recent TDR isuues so I may have to dig out these past issues and take a look.



Regards, John

 

[Bob4x4]

The blend door and recirc door are not the same

 

[JPul]

Bob4x4,



I understand that but I thought I had read about broken blend doors as well, and when the box was apart to fix the recirc door, the blend door function might be very evident.



Regards, John

 

[JPul]

I just looked through my past issues and found Doug Leno's analysis of the HVAC system on page 12 of issue 66. He dismantled his system looking for a problem with the distribution of the air and found it as a stripped drive gear on one of the doors. But he did look at the entire system and analized the various functions and associated pieces.



His system was a single mode system as opposed to the dual climate control. Figure 7 on page 16 clearly shows 2 blend doors controlled by a single actuator. Hence I believe that the coupler from the actuator to the doors, ties the doors together on a single system and that different couplers connect individually to the doors and are driven by separate actuators on a dual mode system.



However, I am getting cooler air out of the passenger side, just not as cold as the drivers side, hence I do not believe that my blend door coupler is broken. Instead, I think the problem is as mentioned previously, that the refrigerant is low and this is backed up by a statement in the manual on page 213 of section 24 (page 9054 0f 9267) on the elctronic version.



But fall is approaching and AC needs are reduced so I may wait till spring.



I do appreciate the assistance.



Regards, John

 

[CharlesHoward]

Possibly I had the same problem, as Passenger side would blow much warmer air than driver's side unless driven for a long time (and all the cabin air was cool).
Took to Dealer today and they added 1 Lb "Freon" and Dye in case this wasn't the fix and there's a leak. Ouch, $149 for diagnosis/labor/supplies/tax...
I used to add "Freon" DITY to my cars but I was hesitant to do so on the BIG truck AC...
Hopefully this fixes the problem of my wife complaining she's too warm, and now she can complain she's too cold !