A/C behaving strangely

JOJO-DFB · 08-21-2008, 02:06 PM

Recently the ac in my 05 5.9 3500 started acting up.
Sometimes the fan won't operate and then kicks in after a while.
The compressor runs fine and the charge pressures look good. Air blows cold too....when the fan works.
I've also noticed that the ac light sometimes stays on with the system off.
Any Ideas?

__________________
2005 3500 5.9 Drw

rthrbelsewhere · 08-21-2008, 02:15 PM

Switch going bad or shorting out somehow? Have you done any work behind the dash in the past that might have caught a wire or something like that? I think i'd check into that first to rule it out.

__________________
'06 Inferno Red 2500 QC, Auto, 285 70 17 BFG AT KO's, Century Ultra Topper, CoolPipe, Icebox w/4091, Amsoil's in da pumpkins and xfer case.

tinkering247 · 08-21-2008, 02:16 PM

probley the high side pressure sender, check the resistance, if its open its nfg

__________________
08 2500 quadcab 4x4 6 spd. manual, edge/attitude"hot", s&b intake, dpf delete, shaved badges, 4" side pipes

tracypouch · 08-21-2008, 02:29 PM

my fan would only blow on high no matter where i put switch.
it turned out radio antena was to close to the fan relay by passenger feet-
moved antena out of the way and been goin good a year...
dealer wanted to put a new relay in for about 400 bones!!

__________________
98.5 4x2 160k quad cab, auto,new ip/lift,silver,bhaf,2 stroke juice,silencer what

Ramtech · 08-21-2008, 07:41 PM

check the wires in back of the ignition switch, I just replaced one Tuesday that had been overheated and melted the wiring. needed an ignition switch, pigtail, and blower motor. just my .02

arcoen · 08-22-2008, 08:10 AM

If your fan only works on high- there is the speed resistor attached to the fan housing where it plugs into the blower fan. That allows acts as a variable resistor for fan speed, and if it blows- only high works .I had to replace mine when it would only work on high.

__________________
2001 extended cab, full bed 2500 4x4 superchiped, 160,000 miles , Running home brewed bio for 7 months- Hauling butt, smelling like french fries- Navy Cummins tech for 15 years

JOJO-DFB · 08-22-2008, 04:04 PM

I appreciate the quick responses.
I've checked all of the switches and relays in the cab. Blower's good too. As is the speed resistor.
The only time it acts up is when the ac compressor light won't turn off when I switch off the fan. Once I've done that the fan won't turn back on but the compressor still cycles.

__________________
2005 3500 5.9 Drw

mark32725 · 08-22-2008, 04:23 PM

The fan is probably coming back on but the evaporator is frozen so no air can pass through it, sounds like the real problem is the compressor is not shutting off from your dash switch...

__________________
1998 Ram 2500 4x4-CTD - Edge - Juice w/Attitude (Hot Unlock)- AirDog 100

JOJO-DFB · 08-22-2008, 04:42 PM

Nope, fan doesn't blow.
It'll also do it first thing in the morning if the light was on when I shut it down the previous night. Engine cold, evaporator warm. I can also do it with the engine off and the key hot and listen for the fan. It's like the ac light is being used as a warning indicator. When the light goes out the condition is clear and I can turn the system back on. I've also unplugged the ac microcontroller and run it as a "dumb" system,same thing (no light though...not plugged in) The fan switch and the microcontroller are separate with a lead out from the fan switch to the m/c to tell it to turn on the compressor. Does anyone know where I can find a detailed electrical scematic?

Thanks guys

__________________
2005 3500 5.9 Drw

08-21-2008, 02:06 PM	#1 (permalink)
JOJO-DFB Newbie Join Date: Aug 2008 Location: Austin Tx. Posts: 3 JOJO-DFB's Truck Pics	A/C behaving strangely Recently the ac in my 05 5.9 3500 started acting up. Sometimes the fan won't operate and then kicks in after a while. The compressor runs fine and the charge pressures look good. Air blows cold too....when the fan works. I've also noticed that the ac light sometimes stays on with the system off. Any Ideas? __________________ 2005 3500 5.9 Drw

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08-21-2008, 02:15 PM	#2 (permalink)
rthrbelsewhere Cummins Nut Join Date: Jan 2007 Location: Greeley, Co Posts: 359 rthrbelsewhere's Truck Pics	Switch going bad or shorting out somehow? Have you done any work behind the dash in the past that might have caught a wire or something like that? I think i'd check into that first to rule it out. __________________ '06 Inferno Red 2500 QC, Auto, 285 70 17 BFG AT KO's, Century Ultra Topper, CoolPipe, Icebox w/4091, Amsoil's in da pumpkins and xfer case.

08-21-2008, 02:16 PM	#3 (permalink)
tinkering247 Newbie Join Date: Jul 2008 Posts: 17 tinkering247's Truck Pics	probley the high side pressure sender, check the resistance, if its open its nfg __________________ 08 2500 quadcab 4x4 6 spd. manual, edge/attitude"hot", s&b intake, dpf delete, shaved badges, 4" side pipes

08-21-2008, 02:29 PM	#4 (permalink)
tracypouch Cummins Fan Join Date: Feb 2008 Location: Winnie TX Posts: 58 tracypouch's Truck Pics	my fan would only blow on high no matter where i put switch. it turned out radio antena was to close to the fan relay by passenger feet- moved antena out of the way and been goin good a year... dealer wanted to put a new relay in for about 400 bones!! __________________ 98.5 4x2 160k quad cab, auto,new ip/lift,silver,bhaf,2 stroke juice,silencer what

08-21-2008, 07:41 PM	#5 (permalink)
Ramtech Tech Specialist Join Date: May 2008 Location: Del Rio, TX Posts: 346 Ramtech's Truck Pics	check the wires in back of the ignition switch, I just replaced one Tuesday that had been overheated and melted the wiring. needed an ignition switch, pigtail, and blower motor. just my .02

08-22-2008, 08:10 AM	#6 (permalink)
arcoen Cummins Fan Join Date: Jan 2008 Posts: 54 arcoen's Truck Pics	If your fan only works on high- there is the speed resistor attached to the fan housing where it plugs into the blower fan. That allows acts as a variable resistor for fan speed, and if it blows- only high works .I had to replace mine when it would only work on high. __________________ 2001 extended cab, full bed 2500 4x4 superchiped, 160,000 miles , Running home brewed bio for 7 months- Hauling butt, smelling like french fries- Navy Cummins tech for 15 years

08-22-2008, 04:04 PM	#7 (permalink)
JOJO-DFB Newbie Join Date: Aug 2008 Location: Austin Tx. Posts: 3 JOJO-DFB's Truck Pics	I appreciate the quick responses. I've checked all of the switches and relays in the cab. Blower's good too. As is the speed resistor. The only time it acts up is when the ac compressor light won't turn off when I switch off the fan. Once I've done that the fan won't turn back on but the compressor still cycles. __________________ 2005 3500 5.9 Drw

08-22-2008, 04:23 PM	#8 (permalink)
mark32725 Cummins Fan Join Date: Jan 2008 Location: Florida Posts: 44 mark32725's Truck Pics	The fan is probably coming back on but the evaporator is frozen so no air can pass through it, sounds like the real problem is the compressor is not shutting off from your dash switch... __________________ 1998 Ram 2500 4x4-CTD - Edge - Juice w/Attitude (Hot Unlock)- AirDog 100

08-22-2008, 04:42 PM	#9 (permalink)
JOJO-DFB Newbie Join Date: Aug 2008 Location: Austin Tx. Posts: 3 JOJO-DFB's Truck Pics	Nope, fan doesn't blow. It'll also do it first thing in the morning if the light was on when I shut it down the previous night. Engine cold, evaporator warm. I can also do it with the engine off and the key hot and listen for the fan. It's like the ac light is being used as a warning indicator. When the light goes out the condition is clear and I can turn the system back on. I've also unplugged the ac microcontroller and run it as a "dumb" system,same thing (no light though...not plugged in) The fan switch and the microcontroller are separate with a lead out from the fan switch to the m/c to tell it to turn on the compressor. Does anyone know where I can find a detailed electrical scematic? Thanks guys __________________ 2005 3500 5.9 Drw