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Ram 1500 HVAC control


Randy Mallory's Avatar
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Join Date: Sep 2001
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VA

05-15-05, 11:42 AM   #1  
Ram 1500 HVAC control

Hello,

I've been fairly active on this site, but this is my first time on the automotive forum. I'm kinda anxious to give it a try.

I have a 94 Dodge full size pickup. For several years, I've had problems with the vacuum control for the HVAC system. Every time I load the engine in the least, the AC disappears from the vent ducts. I have replaced the check valve, although it checked out ok when I removed it. Every time I disturbed anything, it would seem to work for awhile, until recently. I finally broke down and purchased a vacuum tester (pump with gage).

I found out that, if I tried to introduce a small amount of vacuum, it would leak (this is on the control side of the check valve). If I manage to get it passed a certain point, it would seal and hold ok. I feel this may be because the vacuum is pulling two sealing surfaces together. By pinching the hoses in various places, I believe I have narrowed it down to the control itself. If I pinch the vacuum source at the valve...no leak. Pinching any of the other hoses has no effect...it still leaks. By changing the switch selections, the leak rate changes to some degree, but it still leaks.

Bottom line, before I spend $125 for a new control, I wonder if anyone on this forum may have some experience with this system and could make me feel more comfortable spending the money.

Thanks for your help,

 
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05-15-05, 12:33 PM   #2  
What size of vacuum check valve did you replace with?, same size(about an inch in diameter and an inch long) or the bigger one which about 3x bigger than the original one?.

You can also install two valves in there as if the leak (somewhere/control head) is small, make sure install them correctly as they're oneway check valve and see if it's helps.

 
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05-15-05, 12:56 PM   #3  
New guy,

Thanks for the quick reply. I replaced the check valve with an exact replacement from the Dodge dealer. It's about 1.5" diameter and maybe 2.5" long. It is installed correctly. In fact, I tested it out of the circuit and it holds vacuum on the control side. However, with the vacuum pump/gage connected directly into the control side (plugged in where the control side of the check valve would normally be and the check valve out of the circuit, it will not hold a vacuum. If I pinch the tube right where it feeds the control switch/valve, it stops the leak.

Thanks again,

 
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05-15-05, 05:06 PM   #4  
When the A/C changing mode (disappears from vent), where does it blows at?, to defrost mode or to foot mode?.

The vacuum gauge may not holding the vacuum due to the way the actuator works, vacuum must be contanstly present for the actuator stays in it position, once changing to different mode, the actuator will returns to it rest position (bleed hole).

Most of time, if the mode is changes from vent to defrost under load, the vacuum check valve is more likely a problem, if it's changes from vent to floor, mode door actuator on the bottom of A/C heater box is the cause and if it's blows to defrost only at idle regardless where your setting at, it's a control head problem.

 
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05-15-05, 05:22 PM   #5  
Thanks again for the reply.

It definitely changes to defrost. This is the mode that would be expected if the vacuum bleeds off. However, when I apply a vacuum to the control side of the check valve, when it is isolated from the control circuit, it will hold all day. When I apply a vacuum to the control head, it will not hold even when I clamp off every tube leading to/from the head. The only exception, of course, is when I clamp off the tube that goes to the check valve. That stops the leak.

Again, thanks,

 
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05-18-05, 04:26 AM   #6  
New guy,

I am reporting back to thank you for responding and to update anyone who has read throught this thread. I received the control assembly and installed. Good news...it FIXED the problem.

I am happy that I didn't waste my money ($132), but I'm tellin' you, this system proves beyond a doubt that Mickey Mouse is alive and well.

Thanks,

 
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05-19-05, 03:00 AM   #7  
Thank-you.

 
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