Calling all you HVAC experts

[mwilson]

Thanks for checking Bill, I hated to add to my subscription just to check it out as I have the FSM on CD for my '97 and '06 trucks.



I use the ALLDATA-DIY subscription for the Town and Countries that my wife insists on for her transportation.



Figured it was worth a shot, sometimes ALLDATA consolidates and simplifies procedures for the consumer.



Mike.

 

[FFL8N]

I'm pretty sure that the blend doors calibrate themselves. That is one of the problems because as they go through the motion, the plastic pieces get broken during the calibration. The motors are too strong for the plastic end pieces.

 

[SDrake]

They recalibrate every time you turn the key on. If yours isn't working it is either in a bind or something is not assembled correctly. That motor just turns until it sees a load (increased curret draw) then knows how far to turn in the opposite direction to put the door in the other position.

 

[Bill Stockard]

That motor just turns until it sees a load (increased curret draw) then knows how far to turn in the opposite direction to put the door in the other position.

Except the blend door (single control) or blend doors (dual control) open and close to varying degrees depending on where the temperature rotary knob (single control) or slider switches (dual control) are set on the control module. IIRC, that is the door(s) that is calibrated/re-calibrated with the DRBIII scan tool. I have looked in the Factory Service Manual and in ALLDATA-DIY and haven't been able to find the procedure using the DRBIII.



Bill

 

[SDrake]

Except the blend door (single control) or blend doors (dual control) open and close to varying degrees depending on where the temperature rotary knob (single control) or slider switches (dual control) are set on the control module. IIRC, that is the door(s) that is calibrated/re-calibrated with the DRBIII scan tool. I have looked in the Factory Service Manual and in ALLDATA-DIY and haven't been able to find the procedure using the DRBIII.



Bill

OOPs I was thinking only of the recirc door. Will the blend door not operate at all until it is recalibrated with the scan tool?

 

[Bill Stockard]

Mark and Mike,



I found it, finally on ALLDATAdiy.com. I had a few minutes this afternoon and decided I'd look for it one more time. Using the menu, I went right to it... I don't know why I didn't find it yesterday.



The doors are recalibrated with the DRBIII scan tool. Set the DRBIII scan tool menu to: HVAC, System Tests, HVAC Door Recalibration.



Bill

 

[DClark]

HVAC problems on 3rd gen

Actuators recalibrate on their own. Your can ck the actuator with a 9 volt bat. I had the same problem with my '05. It was the control unit. Bought one from a recycler. Works great now.





'96 4X4 lb qc -350K

'98. 5 4X4 lb qc- 175K

'05 4X4 lb qc -160K

 

[Mark.Smith]

Mark and Mike,



I found it, finally on ALLDATAdiy.com. I had a few minutes this afternoon and decided I'd look for it one more time. Using the menu, I went right to it... I don't know why I didn't find it yesterday.



The doors are recalibrated with the DRBIII scan tool. Set the DRBIII scan tool menu to: HVAC, System Tests, HVAC Door Recalibration.



Bill

Thanks Bill!!

 

[Mark.Smith]

Actuators recalibrate on their own. Your can ck the actuator with a 9 volt bat. I had the same problem with my '05. It was the control unit. Bought one from a recycler. Works great now.





'96 4X4 lb qc -350K

'98. 5 4X4 lb qc- 175K

'05 4X4 lb qc -160K

I did check the actuators with a 9volt and they work. If the control unit is bad, would it still actuate the recirc door? My recirc door still works via the dash knob.

 

[KMcBride]

I had nearly the same problem on my 05. I pulled the dash and everything looked good. My recirc door and the blend doors were working, however I only had air coming out of the dash vents. I put a meter on the wires going to the servo motors that move the doors that send air to the floor vents and the defrost vents. I found there was no power going to the servo motors that move those doors.



I felt that the problem was in the control unit on the dash. I pulled the dash controller apart and I could not find any burnt components or damage. I went ahead and replaced the control unit on the dash and now everything works like it should.

 

[Mark.Smith]

I had nearly the same problem on my 05. I pulled the dash and everything looked good. My recirc door and the blend doors were working, however I only had air coming out of the dash vents. I put a meter on the wires going to the servo motors that move the doors that send air to the floor vents and the defrost vents. I found there was no power going to the servo motors that move those doors.



I felt that the problem was in the control unit on the dash. I pulled the dash controller apart and I could not find any burnt components or damage. I went ahead and replaced the control unit on the dash and now everything works like it should.

Do you have to take the dash out to replace the control unit?

 

[KMcBride]

No I did not have take out the dash to replace the control unit. Removing the control unit is like removing the radio. I had to remove the the plastic shrouding surrounding the radio. The whole procedure takes less then a half hour.



Much less work then removing the entire dash.

 

[Mark.Smith]

No I did not have take out the dash to replace the control unit. Removing the control unit is like removing the radio. I had to remove the the plastic shrouding surrounding the radio. The whole procedure takes less then a half hour.



Much less work then removing the entire dash.

Thanks for the post, I just ordered a new control unit and hopefully that will finally fix the problem!

 

[KMcBride]

Good luck there Mark I hope that's the fix. I know where I live a defroster is a must.

 

[Mark.Smith]

Got the new control unit today and installed it and all is good!! Nice to have defrosters and heat on my feet!!

 

[nauidvr1]

Mark. Smith,
Can you provide me a part number for the control unit you replaced on the 2005? I'm having same issue.

I'm having the same problem going on two winters now. I have flushed the system several times, flushed the heater core, used Prestone Super Flush and drove truck with flush chemical in system for 10 hours. I have flushed the system so many times, I know its clean. Changed the thermostat. I have even used a clear discharge hose to inspect all fluid flushes as they were coming out of radiator. I have captured over 60 gallons of my flush water and all of it is clean as a whistle! I have replaced all my air box doors (Re-Circ, Mode 1, Mode 2 & Blend Doors) with the metal ones made by Heater Treater dot net.

I'm at my wits end and I'm literally freezing in my cab!

 

[Mark.Smith]

Mark. Smith,

Can you provide me a part number for the control unit you replaced on the 2005? I'm having same issue.



I'm having the same problem going on two winters now. I have flushed the system several times, flushed the heater core, used Prestone Super Flush and drove truck with flush chemical in system for 10 hours. I have flushed the system so many times, I know its clean. Changed the thermostat. I have even used a clear discharge hose to inspect all fluid flushes as they were coming out of radiator. I have captured over 60 gallons of my flush water and all of it is clean as a whistle! I have replaced all my air box doors (Re-Circ, Mode 1, Mode 2 & Blend Doors) with the metal ones made by Heater Treater dot net.



I'm at my wits end and I'm literally freezing in my cab!

PM sent! For anyone else that's interested, the PN is 55056321-AE.

 

[nauidvr1]

Thanks much!

 

[nauidvr1]

Just an update on my heater issue - still not solved -might help someone else also having this problem.



I replaced the Control unit and still had no heat. Pulled the water pump to see if the impeller was spinning on the shaft - it wasn't, couldn't budge it. I was at my wits end, and went to a Dealer to have the HVAC doors re-calibrated with the DRBIII Scan Tool, since this was the only thing I had not done. They tested the whole system and the actuator motors too. Nice thing is, they only charged me a $30 diagnostic fee!



Dealer seems to think the heater core is the issue. They are saying it is possible that the heater core has good flow, but several of the channels could be blocked. In other words - the heater core is like a radiator in design and I could have good flow because the water entering (when flushing or during normal operation) maybe be able to pass thru a few clear channels, unrestricted, near the beginning of the core and exit, which would look like a good flowing heater core, but not allow a good radiation of heat because it's not flowing thru the whole heater core. One thing I did find out is that the passenger side is blowing "warmer" air than the drivers side, even though I cut out the divider in the air box. This does lend some truth to there theory of a partially blocked heater core, thinking that by the time the air makes it to the drivers side vents it has cooled back to ambient temp, while the path to exit the passenger vents may be shorter and a small amount of heat can be felt. Or that the passenger side of the heater core actually does have some channels that the hot water is flowing thru, but the drivers side has none.



The tech's suggestion was that I remove the heater core hoses and with the heater core filled with water, blow air (at about 25-30 psi) through the heater core, both forwards and backwards several times. Also, to hold a shop rag over the discharging hose to capture any particulates (if any) to see if I am getting any thing out. He also said I could also attempt to use some kind of chemical to assist in breaking things loose, by filling the core with it and letting it sit for 30 minutes then blowing out with air again, both forward & backwards. He said that he has done this a few times before and was successful.



If that doesn't work, then it looks like a heater core for me.

 

[jjdiesel]

How much is a new heater core?