A/C or Fan Problem?
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From: Orland USA
A/C or Fan Problem?
Ok.........My A/C works great but when I have my foot down on the Gas I cannot feel the fan blowing cold air through the vents. But when I let up on the gas it starts blowing throught the vents. 
Is it the fan not working or something closing off the vent?
Or something else????
Thanks,
Jay
Is it the fan not working or something closing off the vent?
Or something else????
Thanks,
Jay
Elder User
Joined: Aug 2003
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From: Houston, TX
what you are experiencing is perfectly normal. I'll quote from the EVTM:
The WOT Cutout Relay is energized by a signal from the EEC Module. This signal opens up the relay's contacts to stop compressor operation during WOT conditions. The EEC Module signals the Relay to open when the engine needs more power or overheats.
The WOT Cutout Relay is energized by a signal from the EEC Module. This signal opens up the relay's contacts to stop compressor operation during WOT conditions. The EEC Module signals the Relay to open when the engine needs more power or overheats.
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From: Georgia
That's close. But there is more to it than that.
What you are experiencing is a lack of vaccum. It's a vaccum switch that controls the damper that directs the air out of the vents. Pressing down on the accelerator will engage the WOT but the vaccum drops too.
If you look you will see that the air is still blowing but it is coming out of the defroster blowing on the windshield. My 94 4.0 is worse about this than my 96. It could be a small vaccum leak in the old hoses. I also had the same problem on the old 91 I used to have. I'm not sure how common this is but I've had to deal with it on at least two vans.
You could spend a lot of time trying to track down every little vaccum leak and fix it or live with it. It's only temporary and comes back when you let up on the throttle.
Your choice.
What you are experiencing is a lack of vaccum. It's a vaccum switch that controls the damper that directs the air out of the vents. Pressing down on the accelerator will engage the WOT but the vaccum drops too.
If you look you will see that the air is still blowing but it is coming out of the defroster blowing on the windshield. My 94 4.0 is worse about this than my 96. It could be a small vaccum leak in the old hoses. I also had the same problem on the old 91 I used to have. I'm not sure how common this is but I've had to deal with it on at least two vans.
You could spend a lot of time trying to track down every little vaccum leak and fix it or live with it. It's only temporary and comes back when you let up on the throttle.
Your choice.
Postmaster
Joined: Sep 2003
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From: Southern California
I'm with Tom, but I would also add that that those vacuum motors (as they are called) do leak a little with old age. It has happened to my other cars often enough that when it happens I just replace them. The worst offenders are Dodge vans 
Every single Dodge van I ever had developed this problem eventually.
Every single Dodge van I ever had developed this problem eventually.
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I'll vote vacuum problem as well. I seem to recall most of the postings on this problem involved the white colored vacuum lines near the firewall. Those seem to deteriorate with age and exposure more quickly than the black rubber ones. I would check those first as they are generally the easiest to get to.
Last edited by aerocolorado; Sep 22, 2004 at 04:25 PM.
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From: Southern California
Hi Aero:
Would you please elaborate a little more on the "white vacuum line near the firewall?" Is it on the engine compartment side or in the passenger compartment side of the firewall?
I don't have this problem yet, but considering the age of my vans, I'm sure it'll come up some day, and it's good to know.
Thanks
Would you please elaborate a little more on the "white vacuum line near the firewall?" Is it on the engine compartment side or in the passenger compartment side of the firewall?
I don't have this problem yet, but considering the age of my vans, I'm sure it'll come up some day, and it's good to know.
Thanks
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The bulk of the problems have been with the whitish colored vacuum tubing located on the passenger side of the engine compartment - the tubing leading to/from the vacuum reservoir as well as the vacuum motor in the engine compartment that opens/closes the fresh air diversion door. (Operates only on MAX A/C)
JTHill24, when this occurs, put your hand near the Defrost vents under the edge of the windshield and see if you feel the air coming out there. If so, the problem is a lack of vacuum as discussed above. Defrost is the default setting for the vacuum controlled system.
JTHill24, when this occurs, put your hand near the Defrost vents under the edge of the windshield and see if you feel the air coming out there. If so, the problem is a lack of vacuum as discussed above. Defrost is the default setting for the vacuum controlled system.
Last edited by aerocolorado; Sep 22, 2004 at 05:25 PM.
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From: Orland USA
Went and checked the white hose and found no breaks or cracks. Traced it beack to a inline valve or filter that connected to a larger black hose that went to the Vacuum Tee.
Check and didn't find anything loose or cracked. The Engine runs and Idles great.
Now what?
Jay
Check and didn't find anything loose or cracked. The Engine runs and Idles great.
Now what?
Jay
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Postmaster
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The problem still sounds like loss of vacuum. Finding a leak is not easy. I would suggest at this point to rent/buy a vacuum tester, pull a vacuum line that feeds the HVAC system, put it under vacuum and see if the vacuum holds steady. I'm betting it will not, meaning you have a leak. Sometimes the local AutoZone or Checker will help you with this if you wait and catch them during a lull in business.
As copper_90680 mentioned, the vacuum motors often develop leaks. There is a vacuum motor in the engine compartment that operates the fresh air door. Depending upon your model and how the motor is mounted it can and does accumulate road grit which eventually wears out the rubber diaphram. Might be a good idea to just pull the vacuum line to this motor, plug it temporarily and see if this cures the problem. The motor only works on the MAX A/C anyway.
As copper_90680 mentioned, the vacuum motors often develop leaks. There is a vacuum motor in the engine compartment that operates the fresh air door. Depending upon your model and how the motor is mounted it can and does accumulate road grit which eventually wears out the rubber diaphram. Might be a good idea to just pull the vacuum line to this motor, plug it temporarily and see if this cures the problem. The motor only works on the MAX A/C anyway.