Heater only blows defrost...
Thread Starter
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Junior User
Joined: Jun 2009
Posts: 97
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Heater only blows defrost...
Hey all,
My truck's blower is stuck on defrost, it does not blow to any other location however I feel the switch is fine because it still works for on/off operation. I've never taken the dash off, how does the system regulate where the air is sent? Is there some kinda flapper controlled with a servo or similar?
One other hunch I have is the Blower Motor Relay... does this sound like a possibilty?
Any help would be greatly appreciated since I don't have much idea on where to start diagnosing this.
I have attached what Chiltons considers a wiring diagram lol...
http://www.frontiernet.net/~burlroof/forumpics/Wiring%20Diag.jpg
Thanks,
Beefey
My truck's blower is stuck on defrost, it does not blow to any other location however I feel the switch is fine because it still works for on/off operation. I've never taken the dash off, how does the system regulate where the air is sent? Is there some kinda flapper controlled with a servo or similar?
One other hunch I have is the Blower Motor Relay... does this sound like a possibilty?
Any help would be greatly appreciated since I don't have much idea on where to start diagnosing this.
I have attached what Chiltons considers a wiring diagram lol...
http://www.frontiernet.net/~burlroof/forumpics/Wiring%20Diag.jpg
Thanks,
Beefey
Thread Starter
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Junior User
Joined: Jun 2009
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Truck: 2002 7.3 4x4
A vac. leak to the front could cause the switching action to fail? The system is dependant on vac pressure to switch blow locations? How would one go about testing this theory?
A vac. leak to the front could cause the switching action to fail? The system is dependant on vac pressure to switch blow locations? How would one go about testing this theory?
Hotshot
Joined: Jan 2008
Posts: 13,144
Likes: 11
From: Rochdale MA
The blend door actuator is vac operated if you have a vac leak the door defaults to the defrost position. Pinch off the lines going to your ESOF system one at a time when the door moves that is the line that needs replacing. This is a very common thing that happens to these trucks. Which is why some of us chose to go with manual lockers 
Lead Driver
Joined: Dec 2006
Posts: 7,092
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From: San Diego, CA
If it's a vacuum leak then it is most likely BEFORE the ESOF system. The ESOF solenoid only sends a brief (30-40 second) vacuum pulse to the hubs to lock or un-lock the hubs. Once the solenoid shuts the blend door will re-align once vacuum builds back up when the pump actuates to restore the vacuum level.
If it is the ESOF system, then he has at least two problems. One is a failed open solenoid valve and the other is a leak in the system that would allow the vacuum to bleed off and never build up to actuate the blend door to another position (the blend door defaults to defrost only for 0" of vacuum).
Just my .02
If it is the ESOF system, then he has at least two problems. One is a failed open solenoid valve and the other is a leak in the system that would allow the vacuum to bleed off and never build up to actuate the blend door to another position (the blend door defaults to defrost only for 0" of vacuum).
Just my .02
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Junior User
Joined: Feb 2005
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From: Michigan
It could also be the Vac pump itself not sure if they are all in the same location but mine is on the passenger side inner fender. You can here it run when you first turn the key on if you are under the hood and have a helper turn the key on.
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Lead Driver
Joined: Dec 2006
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From: San Diego, CA
I don't know what engine beefey has (not listed in his profile), but I think only the diesels have a vacuum pump. The gassers get vacuum from the engine IIRC.
Lead Driver
Joined: Jan 2007
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From: Kiowa CO
Lead Driver
Joined: Dec 2006
Posts: 7,092
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From: San Diego, CA
If it's constantly at defrost, the vacuum leak is UPSTREAM of the solenoid (unless he has a bad solenoid AND a leak in the ESOF, or the vacuum pump itself and its associated lines).
A quick test would be to disconnect your vacuum line from the ESOF solenoid (which is on the fender wall just above the right front wheel well) and plug that line (could be a friend that holds their thumb over the opening). Turn on the truck and see if you can get something besides defrost. If you have normal ventilation control, you have multiple ESOF issues. If you still have your defrost only issue, you have a vacuum leak in your HVAC system (bad pump, bad lines to/from the reservoir, etc.).
Hope this helps.
A quick test would be to disconnect your vacuum line from the ESOF solenoid (which is on the fender wall just above the right front wheel well) and plug that line (could be a friend that holds their thumb over the opening). Turn on the truck and see if you can get something besides defrost. If you have normal ventilation control, you have multiple ESOF issues. If you still have your defrost only issue, you have a vacuum leak in your HVAC system (bad pump, bad lines to/from the reservoir, etc.).
Hope this helps.
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Junior User
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Ok guys this is all good info! I know I have a vac. pump however I don't have auto-locking hubs. They are manual but there is still a selector dial in the cab. This means that obviously it cannot be the ESOF because I dont have one, correct?
If my vac. pump was out wouldn't I have full brake failure? They are completely operable.
Thanks,
Beefey
If my vac. pump was out wouldn't I have full brake failure? They are completely operable.
Thanks,
Beefey
Posting Guru
Joined: Dec 2003
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From: NW Arkansas
Ok guys this is all good info! I know I have a vac. pump however I don't have auto-locking hubs. They are manual but there is still a selector dial in the cab. This means that obviously it cannot be the ESOF because I dont have one, correct?
If my vac. pump was out wouldn't I have full brake failure? They are completely operable.
Thanks,
Beefey
If my vac. pump was out wouldn't I have full brake failure? They are completely operable.
Thanks,
Beefey
Junior User
Joined: Feb 2005
Posts: 92
Likes: 0
From: Michigan
On diesels the power boost for the brakes is from the power steering pump not vacuum. The vac pump is only for heater controls, ESOF and maybe a few other things but not brakes. If you have a dial on the dash your truck originally had ESOF so it is possible that something in the system is still intact and now leaking depending on how much they removed when switching to manual hubs.
Tuned
Joined: Oct 2009
Posts: 292
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From: Raleigh
This is what happened to me. Solenoid stayed open, pump ran continuously, and pump finally gave up. Check the lines to the hub while you're at it. Look for cracks or splits in the lines, and make sure all the connections are secure.