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Topic: No High Speed Fan on Dash Vent (Read 1216 times) previous topic - next topic

No High Speed Fan on Dash Vent

My dash ac blower only works on low speed. Is this black box (see attached picture), located in the center of the dash (on the side of the center front dash storage area) the resistor for the high speed blower?

I replaced the three position fan switch last year. I also replaced a yellow relay that is somehow related to the blower system. Those two items did not fix anything, I subsequently found a loose power wire in the wiring harness going to the blower. High speed worked fine for the next nine months.

Any additional thoughts are welcome.

Thank you



[fixed typo in topic title - Michelle]
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel

Re: No High Spped Fan on Dash Vent

Reply #1 –
I don't know if they are the same, but the high speed on mine has a relay that only operates for the high speed position.  It's a standard auto relay.  I had an issue where only on high the blower would go on and off intermittently.  A new relay solved it.
John Fitzgerald
1991 U300 (SAI) Side Aisle Island Bed 40'
Detroit 6V92 with Allison Retarder
Meridian (Boise), Idaho

Re: No High Spped Fan on Dash Vent

Reply #2 –
On mine it's a bridge rectifier. Replacing it fixed my speed problem.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: No High Spped Fan on Dash Vent

Reply #3 –
Tom,

Can you tell me where the bridge rectifier is located?  I've been fighting a fan problem for years.

Thanks,

Rich
Rich and Peggy Bowman
2002 U270 3610 WTFS, build #5939--"Freedom"
2022 Jeep Grand Cherokee Summit 4xe
SMI AirForceOne brake system
PakCanoe 15

Re: No High Spped Fan on Dash Vent

Reply #4 –
Tom, are you saying the black box in the picture is the bridge rectifier? Did you have to get the new part from Foretravel or was it available locally?

Thank you
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel

Re: No High Spped Fan on Dash Vent

Reply #5 –
Mine was replaced by FOT. It's a very common electronic part. Located under the false floor of the under dash center compartment.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: No High Spped Fan on Dash Vent

Reply #6 –
This is what it looks like. Don't know the voltage and current ratings used.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: No High Spped Fan on Dash Vent

Reply #7 –
I have the same problem.  No high speed on the fan.  I have a 99 model 270.  Does anyone know where the high speed relay is mounted.  I don't have a print showing the relay, so I don't know the wire numbers to the relay.  Any help would be appreciated.  I am not trying to hijack the OP.  I just thought that since the problem is the same maybe the info. will help us both.
Thanks.
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: No High Spped Fan on Dash Vent

Reply #8 –
My problem was the high speed fan relay.  I found it by removing the panel in front of the accelerator and brake pedal.  It was basically hanging near the floor.  I believe it had a couple orange wires, a couple of red wires and a black wire going to it.  While the relay fixed the high blower I think I will have to change the pigtail and connector soon due to heat.
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: No High Spped Fan on Dash Vent

Reply #9 –
Let me add this in case it helps anyone else.  Here is a copy of the schematic I got from FOT.

Rich
Rich and Peggy Bowman
2002 U270 3610 WTFS, build #5939--"Freedom"
2022 Jeep Grand Cherokee Summit 4xe
SMI AirForceOne brake system
PakCanoe 15

Re: No High Spped Fan on Dash Vent

Reply #10 –
Quote from: Rich Bowman –
Let me add this in case it helps anyone else.  Here is a copy of the schematic I got from FOT.

Rich

Awesome share!

I've put a copy in the Media section under Dash AC/Heat  The selected media item is not currently available.
Learn every day, but especially from the experiences of others. It's cheaper!  - John C. Bogle

2000 U320 36' non-slide / WildEBeest Rescue
2003 U320

Re: No High Spped Fan on Dash Vent

Reply #11 –
Thanks Michelle.

It looks to me like the three bridge rectifiers in the center of the drawing in a vertical stack probably control the fan speed.  I'm pretty sure the 12 in a horizontal row control the 7 blend valves.  I think they are shown with a horizontal row of 7 solenoids and below them is a row of 7 actuators.

Tom Lang's picture and comment above helped me a lot to understand what I was looking at on the drawing and under the dash.  If anyone else has any insight, please share.

Rich
Rich and Peggy Bowman
2002 U270 3610 WTFS, build #5939--"Freedom"
2022 Jeep Grand Cherokee Summit 4xe
SMI AirForceOne brake system
PakCanoe 15

Re: No High Speed Fan on Dash Vent

Reply #12 –
If it's a bridge rectifier should be easy to check it with a volt meter that has a diode function. If any show bad,  replace. I had FOT replace my switch and temp control switch last year.
'99 U320 40 WTFE
Build #5462,
1500 Watts Solar 600 amp Victron lithium
2012 Jeep Grand Cherokee Overland Hemi
Instagram bobfnbw
Retired

Re: No High Speed Fan on Dash Vent

Reply #13 –
I called SGM today. I talked to Sean in the tech support area. He was very helpful. My dash was torn apart because I thought I would be replacing the resistor on the the blower motor. When I had the dash (mainly need the center storage area removed, which does require removal of the dash top first) removed and the entire SGM system was clearly visible I found a melted wire in the 6 gang connector (orange wire). I temporarily fixed this connection and my high speed started working, but no medium speed yet. Sean walked me through a couple of voltage checks and we concluded that one of the diode bridges was bad. I disconnected the two solid yellow wires (mark which wire is one the positive side of the bridge) and then jumped between the two wires.  In this temporary arrangement all three fan speeds work. I ordered two new diode bridges (one for spare part) and a new male/female 6 gang connector from SGM. 

The bad diode bridge is the third one down in the vertical stack in the center horizontal row as depicted in the drawing Rich/Michelle attached. It is also the only diode with two solid yellow wires attached.

Now to put the dash back together.  I ended up taking more of the top apart than I needed to.
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel

Re: No High Speed Fan on Dash Vent

Reply #14 –
Ed,

Please take a few pictures as you put things back together.

Thanks

Rich
Rich and Peggy Bowman
2002 U270 3610 WTFS, build #5939--"Freedom"
2022 Jeep Grand Cherokee Summit 4xe
SMI AirForceOne brake system
PakCanoe 15

Re: No High Speed Fan on Dash Vent

Reply #15 –
Rectifiers convert AC current to DC current...have no clue what the application would be in a 12V dash HVAC system.  On my coach, the fan speeds are controlled by this SPAL resistor pack which is mounted on each SGM fan housing.  I may have a couple in a box 'o crap left over from installing the new SGM fans from FOT last year, which came with new resistor packs on em.  Woody.
2001 4010 U320 build #5865 "Bluto-d-Bus" since 09/18
2006 Honda Element ESP Toad
Full timing since 2016 in Western MT
Copilot: Sitka
1975 GMC 260 Avion: sold

Re: No High Speed Fan on Dash Vent

Reply #16 –
I had expected the resistor you pictured to be the problem, but it was one of the diode bridges not allowing the fan to work on medium. The high blower problem was caused by a melted orange wire connector (the melted wire connector possibly the result of a loose connection or a blower motor drawing too much current). Now I know how to take my dash apart!!!

I will post some pictures later.
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel
 

Re: No High Speed Fan on Dash Vent

Reply #17 –
Here are some pictures.
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel