![]() |
Register or Log In To remove these advertisements. |
|
|
![]() |
|
Thread Tools | Display Modes |
![]() |
#1 |
Senior Member
Join Date: Jul 2006
Location: Midlothian TX
Posts: 338
|
Heater Fan doesn't blow on low
A/C cab fan motor doesn't blow on low at all. Will blow on medium sometimes and will blow on high always. Where should I start?
|
![]() |
![]() |
![]() |
#2 |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,818
|
Re: Heater Fan doesn't blow on low
The resistor in the ducting, fan switch and connector on fan switch.
__________________
Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
![]() |
![]() |
![]() |
#3 |
Senior Member
Join Date: Jul 2006
Location: Midlothian TX
Posts: 338
|
Re: Heater Fan doesn't blow on low
|
![]() |
![]() |
![]() |
#4 |
Senior Member
![]() Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,741
|
Re: Heater Fan doesn't blow on low
In the heater core box attached to the firewall inside the cab. Here the box is shown removed and upside down while I was working on it. There is a little door through which you can peek at the resistor board, but to get real access you need to take more apart.
|
![]() |
![]() |
![]() |
#5 | |
Senior Member
Join Date: Jul 2006
Location: Midlothian TX
Posts: 338
|
Re: Heater Fan doesn't blow on low
Quote:
|
|
![]() |
![]() |
![]() |
#6 |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,818
|
Re: Heater Fan doesn't blow on low
What dmjlambert said. In his provided pic you can see two screws, They hold the "S" duct adapter in place. Remove those screws and the ones securing the "S" duct to have access. Not real difficult. The resistor is available at many vendors, here is one of my go to places https://classicparts.com/1964-72-a-c...-w-factory-air
__________________
Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
![]() |
![]() |
![]() |
#7 | |
Senior Member
Join Date: Jul 2006
Location: Midlothian TX
Posts: 338
|
Re: Heater Fan doesn't blow on low
Quote:
|
|
![]() |
![]() |
![]() |
#8 |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,818
|
Re: Heater Fan doesn't blow on low
Look at the heat outlet on the floor above the transmission hump. Left to right- Heat outlet, "S" duct then the fitting screwed the the box shown. As mentioned, pic shows box upside down.
__________________
Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
![]() |
![]() |
![]() |
#9 |
Registered User
Join Date: Dec 2017
Location: Elkhart, Texas
Posts: 1,731
|
Re: Heater Fan doesn't blow on low
Before you start digging around in the heater case, read Richard's post #2 again.. Check the heater switch and/or the plug connecting the wires to it.. Not only a bad resistor, but also a bad switch or corroded/loose connection will cause the symptoms you describe..
|
![]() |
![]() |
![]() |
#10 | |
Registered User
Join Date: Dec 2005
Location: Kalifornia
Posts: 344
|
Re: Heater Fan doesn't blow on low
Quote:
|
|
![]() |
![]() |
![]() |
#11 |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,175
|
Re: Heater Fan doesn't blow on low
It's also possible the AC fan relay is causing problems.
Here are some threads to help. First has some good tests for components https://67-72chevytrucks.com/vboard/...d.php?t=848097 This one is a great discussion on how the AC fan circuit works along with a wiring schematic. http://67-72chevytrucks.com/vboard/s...d.php?t=813743 And one more. https://67-72chevytrucks.com/vboard/...d.php?t=731399
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
![]() |
![]() |
![]() |
#12 | |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,818
|
Re: Heater Fan doesn't blow on low
Quote:
__________________
Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
|
![]() |
![]() |
![]() |
#13 | |
Post Whore
![]() Join Date: Feb 2016
Location: Portland Oregon
Posts: 11,175
|
Re: Heater Fan doesn't blow on low
Quote:
When you have intermittent problems the likely suspects are switches and relays. In the OP's case we shouldn't assume there is only one problem. It is quite likely the failure of the low speed is caused by the resistor especially if all the wiring harness is undamaged. But the intermittent medium speed problem could be caused by bad contacts inside the A/C relay. Just my opinion which with a sawbuck will get you a cup of Joe in most places.
__________________
Thanks to Bob and Jeanie and everyone else at Superior Performance for all their great help. ![]() RIP Bob Parks. 1967 Burban (the WMB),1988 S10 Blazer (the Stink10 II),1969 GTO (the Goat), 1970 Javelin, 1952 F2 Ford OHC six 4X4, 29 Model A, 72 Firebird (the DBP Bird). 85 Alfa Romeo If it breaks I didn't want it in the first place The WMB repair thread http://67-72chevytrucks.com/vboard/s...d.php?t=698377 |
|
![]() |
![]() |
![]() |
#14 |
Registered User
Join Date: Jan 2011
Location: Chattanooga, TN
Posts: 2,152
|
Re: Heater Fan doesn't blow on low
I would also tend to at least take a hard look at the relay. I have replaced a whole bunch more relays than resistors over the years in a wide variety of GM cars and trucks.
__________________
'83 K20-TPI '73 C10 '79 C10-ex-diesel(SOLD) '07 Tahoe(Son driving) '14 Suburban-DD '71 C10-current project |
![]() |
![]() |
![]() |
#15 | |
Senior Member
![]() Join Date: Dec 1999
Location: Southern California
Posts: 2,818
|
Re: Heater Fan doesn't blow on low
Quote:
The third terminal on the relay is the positive side of the energizing coil which connects to the high speed terminal at fan switch. Power only flows through this wire if switch is in high position. The negative side of the coil grounds through the relay case. Just trying to provide help for understanding of how the circuit works.
__________________
Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
|
![]() |
![]() |
![]() |
Bookmarks |
|
|