2nd Gen Non-Engine/Transmission Help finding A/C issue

[RandallScot]

Anyone that has had this issue, or can lead me in a direction to fix this problem, this is what's happening. My A/C works great, until I put the brakes on to stop. At this point, A/C starts blowing hot air. I turn A/C switch off until I start to accelerate, then turn switch back on and BAM, cold air. This happens almost every time I brake. It is pretty hot here, and I am lucky when I toggle the switch, the A/C does come on. Any suggestions are greatly appreciated. By the way, I have a 2000 2500, quad cab.

 

[Stranger]

Have you had any luck fixing the A/C problem? My '02 is doing the same thing.

At first I thought it might be a ground issue but, most folks on this board poo-pooed that. Now, I've been throwing $$$ at it in hopes of hitting it. No luck so far.

I'm kinda looking at the blend door actuator because when it happens, I can hear the blend door slam shut.

 

[HHhuntitall]

Randall, is it blowing out the defrost vents, or just hot out the vents?

If hot out the vents, is it whenever you let off the throttle and it goes to an idle?

 

[RandallScot]

Still exists

As soon as I apply the brake pedal to slow down or stop, hot air starts blowing. One thing I did not mention, when this does happen, I usually must turn off A/C cotrol switch, after acclerating I turn the A/C switch back on and have cold air. This does not happen every time I brake. It also seems if I am going under say 10 MPH and brake, the air continues to blow cold, but anything over and I have the condition. TIA TDR members

 

[HHhuntitall]

That's a pretty weird one. I'm guessing it's a vacuum leak at the moment, preventing the blend door from staying in the correct position, as mentioned above... . The diaphragm actuators are prone to going bad at times. Strange it works at higher throttle position, though. Perhaps a broken vacuum line under the hood. The release of the throttle allows a drop in vacuum due to lower rpms?

 

[fest3er]

That's a pretty weird one. I'm guessing it's a vacuum leak at the moment, preventing the blend door from staying in the correct position, as mentioned above... . The diaphragm actuators are prone to going bad at times. Strange it works at higher throttle position, though. Perhaps a broken vacuum line under the hood. The release of the throttle allows a drop in vacuum due to lower rpms?

This is purely electrical. Electric is the only thing that controls the compressor clutch.



Check all of your ground points. Start with the one by the antilock brake controller on the left side and the one by the battery on the right side.



I suspect that the ground for the brakes is 'not good'. This raises the voltage there for all devices grounded at that point, making other circtuis see less than the nominal 13VDC. There's a slight chance the PCM is involved; hitting the brake sends a signal to the PCM which, due to a faulty ground, may make the PCM think the throttle is wide open and disengage the compressor clutch in response. Since speed is involved, I might suspect the ground point by the antilock brake controller.



When it's dark, apply the brake and see if any other circuits do weird things, like lights getting dimmer.

 

[Sticks]

A specific answer to post #3 will tell the tale here.

Anytime a vacuum failure happens in the HVAC system, the vents default to the defrost vents. If you have the selector switch set to the dash or floor and when you brake you get hot air and the air flow starts coming out the defroster, then it's a vacuum issue.

Verifying that the A/C clutch is still engaged is the second step.

Not unheard of to have two problems going on here either.

 

[HHhuntitall]

This is purely electrical. Electric is the only thing that controls the compressor clutch.

Check all of your ground points. Start with the one by the antilock brake controller on the left side and the one by the battery on the right side.

I suspect that the ground for the brakes is 'not good'. This raises the voltage there for all devices grounded at that point, making other circtuis see less than the nominal 13VDC. There's a slight chance the PCM is involved; hitting the brake sends a signal to the PCM which, due to a faulty ground, may make the PCM think the throttle is wide open and disengage the compressor clutch in response. Since speed is involved, I might suspect the ground point by the antilock brake controller.

When it's dark, apply the brake and see if any other circuits do weird things, like lights getting dimmer.

Verifying the problem is not the simplest is the first step. Then be back trace to the next step. That is a good idea, to check to make sure the compressor is staying engaged. But an immediate change from cold to hot is not electrical. The evaporator stays cold for a minute or two after the compressor is shut off, as pressure on the high side of the system equalizes to the low side, still passing through the orifice, still cooling. So we need to know if the fan is staying on, where is the cool air going? Why is it suddenly hot? Is it allowing hot air to pass through the heater core?

 

[Stranger]

With mine, the fan continues, the HOT air comes out of the vents in the dash, the same vents the cold air was coming out of. No defroster action. I have had it do this after braking, or if I hit a bump. Not a huge bump, either.

If I turn from A/C to off then on, sometimes it cools immediately. But, sometimes it will cool for a half a second or so then goes to hot. On, off, on, off, on, off multiple times gets it working again.

I'm deaf as a post in this ear and can't hear worth a hoot in the other one. However, when this issue happens, I can hear a muted clunk, or thunk. That's why I was thinking the blend door actuator. But now that I think about it, the blend door would of course redirect the air output.

 

[HHhuntitall]

With mine, the fan continues, the HOT air comes out of the vents in the dash, the same vents the cold air was coming out of. No defroster action. I have had it do this after braking, or if I hit a bump. Not a huge bump, either.

If I turn from A/C to off then on, sometimes it cools immediately. But, sometimes it will cool for a half a second or so then goes to hot. On, off, on, off, on, off multiple times gets it working again.

I'm deaf as a post in this ear and can't hear worth a hoot in the other one. However, when this issue happens, I can hear a muted clunk, or thunk. That's why I was thinking the blend door actuator. But now that I think about it, the blend door would of course redirect the air output.

Sometimes, with a bad or worn compressor, they will clunk when they engage. It's prolific on the '03+ trucks, from what I've experienced, but the older trucks will do it, too. I'm curious if your clutch is not slipping on the AC compressor, if you gradually lose the cool air. An immediate blast of hot air would have to be related to the heater core and it's operation.

 

[Stranger]

I hear the clunk then immediate hot air. I can feel down by the box that houses the blend door and the resistor, (which has been changed) and the box is cold.

 

[RandallScot]

Like Stranger, I usually hear the clunk, then immediatly hot air out of all vents.
The control switch is on max air. As stated before, I can toggle control switch, then back to max air within say 30 sec. , and bam, cold air immediatly.
I'm liking the reply from fest3er being an anti-lock ground, reason being this only occurs when I hit my brakes. Thanks guys for all your replies

 

[Stranger]

But, does it happen EVERY time you touch the brakes or only if you hit them with a bit more effort than usual?

That's what mine does.

 

[Demons_Ram]

Randall and others,
Check the old thread listed below.

https://www.turbodieselregister.com/forums/showthread.php?225293-Heater-full-on&highlight=demons_ram

The blend door has nothing to door with which vents the air is coming out of. It only controls temperature blending.

It's possible that your and the others "Blend Door" has broken loose from the interposer (coupling between the blend door lower axle shaft and the servo temp control {actuator motor}) and is just flopping back and forth as you decelerate and accelerate. It looks like under deceleration if the door is swinging free, it would match up to the second picture in post # 2 of the thread above, allowing air to flow through the heater core and exiting hot. Under acceleration the free wheeling door would flop back covering the heater core and you would have the result of the first picture in post # 2 of the thread above.

This is easy to check by looking under the HVAC box inside the truck, on the right side of the transmission hump. You can see the servo motor for the blend door bolted to bottom of the box.

With the truck ignition on, watch the coupling just above the servo as you rotate the air temperature control knob slowly from one extreme to the other. You should see the servo rotating the silver part that comes out of it. The silver part shown below.

If it doesn't rotate then you have a bad servo actuator motor, HVAC control head or a wiring problem. You'll have to diagnose further.

(NOT SHOUTING, JUST EMPHASIZING!!!) It's a very good practice to NEVER, NEVER, NEVER on a newer vehicle, plug in a servo actuator to the wiring, and turn the ignition on without it being connected to the shaft, coupler, or axle that is on the door being actuated that provides positive stops for the actuator. A lot of these, especially in newer vehicles go through a learning process as soon as the key is turned on. It looks for the resistance occurring when the door reaches each end of its travel, and memorizes that so it can kill power to the actuator at each stop and also indexes mid points, so it can accurately correspond to the control head knob/button adjustments.


If the actuator blend door motor rotated, with the ignition now off, remove the servo actuator, grab the interposer, part left sticking down and turn and wiggle the shaft to determine if the blend door inside is still in one piece and travels freely from one extreme to the other. If it is broken inside or frozen you may have to remove the whole HVAC box to replace that assembly or you could try to install Heater Treater's blend door replacement product. to cut the heat off when needed. http://www.heatertreater.net/magento/index.php/core-regulator.html You are still going to have control problems though.

At this point I personally unplugged my Actuator Servo motor from the wiring, cranked the truck and turned the blend door axle shaft by hand to determine if the proper response occurred.

If all was good so far, pull down on the interposer and remove for inspection. These are commonly cracked or split causing the actuator to keep spinning on the blend door axle and/or let the door do it's own thing without control. If split or cracked you can try to repair yourself of order one of the Heater Treater repair products. http://www.heatertreater.net/magento/index.php/dodge/dodge-ram-95-02.html

View attachment 86060

Please post up what you find and the fix, to benefit other TDR members in the future.

 

[RandallScot]

Demons_Ram,
Thanks, I appreciate the info, pics, and all the possible scenerios. Once I find whatever the issue is, I will most gladly reply what the problem was, & what it took to fix. And people say no one communicates anymore, that's cause they are not on TDR ")