A/C and heater control

billk · 06-13-2008, 11:22 AM

The blower in my 88 c2500 only runs on 1 speed ( high)
I have looked for a new control but all the ones listed on eBay are digital this one is mechnical..even the LMC catalog did not list this control
any ideas?..the truck was manufactured in 04 1987 but it is definetly an 88 model...I even looked at 1987 controls but they are different I put a pic of it at the bottom
Thanks
Bill

Case 7230 · 06-13-2008, 12:57 PM

Are you sure it is the control unit? Sounds to me more like a faulty resistor. Unfortunately I don`t know where it is located on your model.

og25 · 06-13-2008, 01:33 PM

Hey billk, I agree with Case it sounds like a resistor. Check and see if it is by the blower motor. The one on my 96 is up under the dash behind the glove box. I looked in a chiltons manual and it looks like your blower motor is under the hood. The resistor is mounted into the housing either by the blower motor or under the dash. It will have an electrical plug attached to it with 3 or 4 wires and 3 or 4 screws holding it in place. When you pull it out it will have what looks like small coil springs on it. I hope that makes sense.

billk · 06-13-2008, 02:09 PM

hi thanks I found the resistor..it was behind the glove box mounted to the top of the heater box..It does not look bad nothing looks burnt how do I test it? or should I just go buy a new one?
I have a vom but dont know what the resistance is supposed to be
Bill

billk · 06-13-2008, 02:33 PM

found one on eBay gm # 15551633 $19.99 plus 7,50 shipping..local GM dealer does not stock it.. just hate to buy one if that is not the problem.. any way to test it?
Thanks

og25 · 06-13-2008, 03:36 PM

Hey billk, You can use your ohm meter to test the resistor! I hope I can explain this so it makes sense. It's not like a fuse it can look ok but still be bad. Look on the side with the resistor springs and try to figure out which resistor springs are attached to the plug prongs on the other side. You should be able to touch one ohm meter probe to the main resistor plug prong ( I believe it will be the one that the dark blue wire attachs to) and the other ohm meter probe to each of the the plug prongs and get a reading on each one. If not it is bad. I hope that makes sense. I bought a new resistor for my 96 about a month ago and it was 40 bucks. Good luck!

billk · 06-13-2008, 04:49 PM

the continuity checks ok on this resistor so maybe my problem is elsewhere..
I read a circuit on all 3 terminals..but I don't know what the actual resistance is supposed to be..this is a 20 year old truck and it appears someone has "fooled" around with the wiring so this may be a tough fix..
The blower runs and the A/C and heater work I just don't like the noise it makes on full blast..I am planning a 1400 mile trip in July and would like to be able to turn this thing to "low"

Thanks for your help
Bill

leolkfrm · 06-14-2008, 10:49 AM

Thougt I posted yesterday! Check the resister with volts the fan is controlled by the amount of volts going to it, therefore less volts less speed. continuity results might mean 12 volts all the time

06-13-2008, 11:22 AM	#1
billk Full Member Join Date: Jun 2008 Posts: 31	A/C and heater control The blower in my 88 c2500 only runs on 1 speed ( high) I have looked for a new control but all the ones listed on eBay are digital this one is mechnical..even the LMC catalog did not list this control any ideas?..the truck was manufactured in 04 1987 but it is definetly an 88 model...I even looked at 1987 controls but they are different I put a pic of it at the bottom Thanks Bill Attached Thumbnails

06-13-2008, 04:49 PM	#7
billk Full Member Join Date: Jun 2008 Posts: 31	the continuity checks ok on this resistor so maybe my problem is elsewhere.. I read a circuit on all 3 terminals..but I don't know what the actual resistance is supposed to be..this is a 20 year old truck and it appears someone has "fooled" around with the wiring so this may be a tough fix.. The blower runs and the A/C and heater work I just don't like the noise it makes on full blast..I am planning a 1400 mile trip in July and would like to be able to turn this thing to "low" Thanks for your help Bill Attached Thumbnails

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06-13-2008, 12:57 PM	#2
Case 7230 Senior Member Join Date: Dec 2007 Posts: 253	Are you sure it is the control unit? Sounds to me more like a faulty resistor. Unfortunately I don`t know where it is located on your model.

06-13-2008, 01:33 PM	#3
og25 Full Member Join Date: Jun 2008 Posts: 23	Hey billk, I agree with Case it sounds like a resistor. Check and see if it is by the blower motor. The one on my 96 is up under the dash behind the glove box. I looked in a chiltons manual and it looks like your blower motor is under the hood. The resistor is mounted into the housing either by the blower motor or under the dash. It will have an electrical plug attached to it with 3 or 4 wires and 3 or 4 screws holding it in place. When you pull it out it will have what looks like small coil springs on it. I hope that makes sense.

06-13-2008, 02:09 PM	#4
billk Full Member Join Date: Jun 2008 Posts: 31	hi thanks I found the resistor..it was behind the glove box mounted to the top of the heater box..It does not look bad nothing looks burnt how do I test it? or should I just go buy a new one? I have a vom but dont know what the resistance is supposed to be Bill

06-13-2008, 02:33 PM	#5
billk Full Member Join Date: Jun 2008 Posts: 31	found one on eBay gm # 15551633 $19.99 plus 7,50 shipping..local GM dealer does not stock it.. just hate to buy one if that is not the problem.. any way to test it? Thanks

06-13-2008, 03:36 PM	#6
og25 Full Member Join Date: Jun 2008 Posts: 23	Hey billk, You can use your ohm meter to test the resistor! I hope I can explain this so it makes sense. It's not like a fuse it can look ok but still be bad. Look on the side with the resistor springs and try to figure out which resistor springs are attached to the plug prongs on the other side. You should be able to touch one ohm meter probe to the main resistor plug prong ( I believe it will be the one that the dark blue wire attachs to) and the other ohm meter probe to each of the the plug prongs and get a reading on each one. If not it is bad. I hope that makes sense. I bought a new resistor for my 96 about a month ago and it was 40 bucks. Good luck!

06-14-2008, 10:49 AM	#8
leolkfrm Senior Member Join Date: Mar 2008 Location: N.Y. Posts: 1,456	Thougt I posted yesterday! Check the resister with volts the fan is controlled by the amount of volts going to it, therefore less volts less speed. continuity results might mean 12 volts all the time