Calling all DC techs

[RedRam1]

I need to tap the vast TDR knowledge base one more time for help with my '98 Grand Caravan! I've learned a bunch about my truck on this site, but you guys have become an invaluable resource when it comes to the wife's van.

Here's my problem: The heater does not work, and it's starting to get cool here in the north GA mountains. The sliding rheostats on the heater control do not have any effect what-so-ever, this has been going on for a while - it was a little irritating back in the summer, not being able to tone down the A/C, but is not going to fly at all in the late fall/winter.

My wife spilled a soft drink all over the controls last spring, and this problem showed up a few weeks later. For this reason, I assumed the problem was in the dash mounted controls, I took this assy out, and sprayed contact cleaner around the sliding controls, this did not help. I decided to check out the valve that controls coolant flow thru the heater core, but could not find where this part was located, it does not appear to be under the hood. Can anyone help me out with the following questions?



1. Where is the coolant control valve?



2. How do I check out the rheostats - there is a ~24 pin connector that plugs into this thing.



3. Any other suggestions?



I suspect the controls or the coolant valve because you cannot get any heat regardless of the position of the selector e. g. heat, ac, defrost. The switching mechanism works properly i. e. the air blows out the right holes, it just won't get hot.



Thanks for any help.



Jim

 

[RedRam1]

Forgot to mention this rig has the 3. 3L motor, if that makes any difference.

 

[kaffine krazed]

It doesn't use a heater control valves anymore. They use a blend door system that either directs air through or around the heater core. The air always goes through the AC evap core. It uses electric motors to control the position of the blend door.



It's been awhile since I've worked on them. There is a way to recalibrate the system. If you have an owners manual it might be listed in it. You have to have the engine on AC on and hold 2 buttons down for 5 seconds but I can't remeber what buttons.

 

[RedRam1]

Kaffine,



Thanks for the advise. I'll check my owners manual & see if there are any instructions to recalibrate the system. If this does not work, how difficult is it to get to the heater core blend door? Is this door actuated by vacuum or electrically?



Thanks,

Jim

 

[Paul Herioux]

Recalibration proceedure

Jim,

To recalibrate the HVAC control head do the following.



1) Start engine and let run until it reaches operating temperature. Leave engine running for all of following.



2) Set blower to high, temp to hot, mode to anything but defrost.



3) The rear wiper and defroster switches are on the left side of the panel. Press and hold the top and bottom switches until all lamps on panel light.



4) Release switches. Calibration sequence will run on its own. If there are no faults in the system the lights will quit flashing and the system will return to normal operation. If there is a fault, the code for it will be flashed on the rear wiper and defroster switches.



HTH's

Let us know how it turns out.

Paul



Former DC tech, 2 1/2 years of bliss and counting.

 

[RedRam1]

Thanks, Paul. I'll run thru your recalibration routine when I get home this evening - sure would be nice if that is all it takes to get the hot air blowing. I will report back with the results tomorrow. It has warmed back up a little, so the wife is not beating on me too bad to get if fixed, but I still need to get it taken care of fairly quickly.

 

[RedRam1]

Paul,



No luck. I tried to initiate the recalibration routine per your instructions, but could not get it to run. I know the problem is not with the buttons on the panel as each button does what it is supposed to. I suspect the problem is with the sliding temp controls on the panel. Bear in mind that my wife doused this panel with coke a little bit before this problem started. Your instructions said to set the temp to hot before running the recalibration routine. I wonder if the computer 'thinks' the control is on cold, would this prevent the routine from running? I also notice that when I change the selector setting, I can hear the acturtor motors running, but when I move the temp controls, nothing happens. The heater core is getting hot, I can feel it thru the case, but obviously the blend doors are completly shut. Do you have any other suggestions?



Thanks,

Jim

 

[Paul Herioux]

Hate to say it Jim, but I think the control head went Three Mile Island on you. These heads are finicky to start with and the Coke probably didn't help. Let's just say that I have had to replace more than a few in my career.

Good luck.

Paul

 

[RedRam1]

Paul,



What exactly do you mean by 'control head'? Is this an assemby installed between the heater core and a/c evaporator assy containing the blend door/door actuator motors and so forth? I'm about to break down and take it to the dealer unless there are any other checks I can perform myself. I have no problems replaceing parts (was a Nissan tech for 6 yrs in the late '70's early 80's), I'm just hesitant to start replacing fairly expensive components without a real high level of confidence that I am attacking the right parts.



Is there anything I can do myself to definitively ascertain if my problem is with the control head?



thanks,

Jim

 

[Paul Herioux]

Jim,

The control head is the part with the A/C /Heater, rear defroster, and rear wiper switches that form the bezel around the radio. The silver box on the backside also contains a small computer module that communicates with the body computer to control the HVAC system.

 

[RedRam1]

Paul,



Well, at least that part is a piece of cake to replace. I'm still debating whether or not to take it to the dealer, or roll the dice and replace the control head myself. Given that the unit crapped out shortly after receiving a Coke bath, I would really be surprised if this is not my problem. However, in the unlikely event the control head did not solve my problem, I assume the dealer would not take it back, and can't say as I would blame him. I'm going to discuss with my dealer later today. I'll let you know how things work out.



Jim

 

[RedRam1]

Paul,



Thought I'd dredge this thread up and let you know the latest: I broke down and purchased a new control head from the dealer, got it for $350 thru one of my buddies who has a dealer contact, my dealer wanted $425.

I tried for several weeks to find a used head from various salvage yards. First thing the salvage guys ask is whether you have a single white, or single blue connector. Mine had the white connector, which apparently is rare as hens teeth, everyone had blue, no one but the dealer had white.

Put the new part in & initiatiated your recallibration routine. Lights flashed on and off on the panel for a minute or so, and everything now works perfectly.

Thanks again for the help, without your instructions on how to callibrate, I would have been lost even with the new part.



Jim