Well, I was just testing some electric fan control on my test bench, and it seems to work exactly as the author says it does.

Just a couple things I want to be able to fine tune, like the actual turn on and off temps, but hopefully will be able to sort that out soon.

Anyway, this is originally from: http://www.fullsizechevy.com/forum/g...n-code-0d.html
Change in code need for $0D:

What this code does

Engine temperature
Below 190F, fan off
Above 199F, fan turns on
above 210F, fan forced on regardless of other conditions

If the vehicle speed is above 25 MPH, the fan turns off unless the 45 seconds has not elapsed, or the temperature is very high (above 210F) in which case the fan will run at any vehicle speed.

The fan is turned on when the A/C Clutch is engaged. Unless the vehicle speed is above 25 MPH.

The code includes a 45 second absolute minimum fan run time. This was the big change from my last code. I added this condition so that if the A/C Compressor is cycling every 10 seconds, its not beating the fan, relay and electrical system up. It was also needed because of the 25 MPH fan rule, where if you were driving along at 24-26 MPH, the fan would cycle with subtle changes in speed. This solved that issue.

You can add the calibrations at locations L7000-L7004 to your preferred editor to allow you to change the values you would like to use for temperature, speed, or even the minimum fan run time using your editor program.

Code:
Ram Variables:    
L02A7 = MPH    
L00A2 = Coolant Temp    
L004D,BIT 0 = A/C STATUS (1 = A/C Requested on)    
L0052,BIT 3 = Fan Output Control    
L0150 = Minimum Fan Run Timer    

To enable this routine, be sure to change the Value at address 7C6F from D399 to 7020    
Connect the fan relay to E3, Connect the other end of the relay coil to Power. The computer GROUNDS E3 to run the fan.    

Coolant temp example:    
199 deg F    
199 + 40 = 239    
239/1.35 = 177.04 (round to 177)    
177 is B1 in hexidecimal.    

Calibrations:    
L7000    19     db     High MPH Fan Cutoff (25 MPH)
L7001    B9     db     Coolant Temperature Very High Value Enable (210 deg F)
L7002    B1     db     Coolant Temperature High Value Enable (199 deg F)
L7003    AA     db     Coolant Temperature Low Value Disable (190 deg F)
L7004    2D     db     Minimum Fan Run "MFR" Time (45 Seconds)

Algorithms:    
L7020    CE    70    00     L7020     LDX    #L7000     Start of fan Calibrations
L7023    12    52    08    1F     BRSET    L0052,#$08,L7046     If Fan is On, Skip to "Load MFR Timer Variable"
L7027    96    A2     LDAA     L00A2     Load Coolant Temperature
L7029    A1    01     CMPA    1,X     Compare to Coolant Temperature Very High Value
L702B    22    11     BHI     L703E     Go to "Turn On Fan" if Higher
L702D    12    4D    01    06     BRSET    L004D,#$01,L7037     If A/C is On, Go To "Load MPH"
L7031    96    A2     LDAA     L00A2     Load Coolant Temperature
L7033    A1    02     CMPA    2,X     Compare to Coolant Temperature High Value Enable
L7035    23    37     BLS     L706E     Go To "End" if Lower
L7037    B6    02    A7     L7037     LDAA    L02A7     Load MPH
L703A    A1    00     CMPA    0,X     Compare to High MPH Fan Cutoff
L703C    22    30     BHI     L706E     Go to "End" if Higher
L703E    14    52    08     L703E     BSET     L0052,#$08     Turn on Fan
L7041    A6    04     LDAA     4,X     Load MFR Timer
L7043    B7    01    50     STAA    L0150     Save MFR Timer to L0150
L7046    B6    01    50     L7046     LDAA     L0150     Load MFR Timer Variable
L7049    26    16     BNE     L7061     If timer is Not Zero go to "Load MFR Timer Variable"
L704B    12    4D    01    06     BRSET    L004D,#$01,L7055     If A/C is On, Go To "Load MPH"
L704F    96    A2     LDAA     L00A2     Load Coolant Temperature
L7051    A1    03     CMPA    3,X     Compare to Coolant Temperature Low Value Disable
L7053    23    09     BLS     L705E     Go To "Turn off fan" if Lower
L7055    B6    02    A7     L7055     LDAA     L02A7     Load MPH
L7058    A1    00     CMPA    0,X     Compare to High MPH Fan Cutoff
L705A    22    02     BHI     L705E     Go To "Turn off Fan" if Higher
L705C    20    10     BRA L706E     End
L705E    15    52    08     L705E     BCLR     L0052,#$08     Turn off Fan
L7061    B6    01    50     L7061     LDAA     L0150     Load MFR Timer Variable
L7064    D6    02     LDAB     L0002     Load Loop Counter
L7066    C4    F0     ANDB     #$F0     Mask First 4 Bits
L7068    26    04     BNE     L706E     Skip To end if no Decrement of Timer Needed
L706A    4A     DECA     Decrease MFR Timer by 1
L706B    B7    01    50     STAA    L0150     Save MFR Timer to L0150
L706E    4F     L706E     CLRA     Clear A Register
L706F    5F     CLRB     Clear B Register
L7070    39     RTS     Return
Here is the code as you would paste it into a hex editor. Just be sure that it OVERWRITES this section when you paste it, or else it will shift the whole program around, and your vehicle will NOT RUN.

Code:
7000: 19 b9 b1 aa 2d 00 00 00 00 00 00 00 00 00 00 00
7010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
7020: ce 70 00 12 52 08 1f 96 a2 a1 01 22 11 12 4d 01
7030: 06 96 a2 a1 02 23 37 b6 02 a7 a1 00 22 30 14 52
7040: 08 a6 04 b7 01 50 b6 01 50 26 16 12 4d 01 06 96
7050: a2 a1 03 23 09 b6 02 a7 a1 00 22 02 20 10 15 52
7060: 08 b6 01 50 d6 02 c4 f0 26 04 4a b7 01 50 4f 5f
7070: 39
Change in code needed for $0E (I haven't tested this yet)

So here it is, The same code, adapted to work for $0E:

Ram Variables:
L0283 = MPH
L00A8 = Coolant Temp
L004D,BIT 0 = A/C STATUS (1 = A/C Requested on)
L0052,BIT 3 = Fan Output Control
L0151 = Minimum Fan Run Timer

To enable this routine, be sure to change the Value at address 7C07 from D567 to 7120
Connect the fan relay to E3, Connect the other end of the relay coil to Power. The computer GROUNDS E3 to run the fan.

Coolant temp example:
199 deg F
199 + 40 = 239
239/1.35 = 177.04 (round to 177)
177 is B1 in hexidecimal.

Calibrations:
L7100 19 db High MPH Fan Cutoff (25 MPH)
L7101 B9 db Coolant Temperature Very High Value Enable (210 deg F)
L7102 B1 db Coolant Temperature High Value Enable (199 deg F)
L7103 AA db Coolant Temperature Low Value Disable (190 deg F)
L7104 2D db Minimum Fan Run "MFR" Time (45 Seconds)

Algorithms:
L7120 CE 71 00 L7120 LDX #L7100 Start of fan Calibrations
L7123 12 52 08 1F BRSET L0052,#$08,L7146 If Fan is On, Skip to "Load MFR Timer Variable"
L7127 96 A8 LDAA L00A8 Load Coolant Temperature
L7129 A1 01 CMPA 1,X Compare to Coolant Temperature Very High Value
L712B 22 11 BHI L713E Go to "Turn On Fan" if Higher
L712D 12 4D 01 06 BRSET L004D,#$01,L7137 If A/C is On, Go To "Load MPH"
L7131 96 A8 LDAA L00A8 Load Coolant Temperature
L7133 A1 02 CMPA 2,X Compare to Coolant Temperature High Value Enable
L7135 23 37 BLS L716E Go To "End" if Lower
L7137 B6 02 83 L7137 LDAA L0283 Load MPH
L713A A1 00 CMPA 0,X Compare to High MPH Fan Cutoff
L713C 22 30 BHI L716E Go to "End" if Higher
L713E 14 52 08 L713E BSET L0052,#$08 Turn on Fan
L7141 A6 04 LDAA 4,X Load MFR Timer
L7143 B7 01 51 STAA L0151 Save MFR Timer to L0151
L7146 B6 01 51 L7146 LDAA L0151 Load MFR Timer Variable
L7149 26 16 BNE L7161 If timer is Not Zero go to "Load MFR Timer Variable"
L714B 12 4D 01 06 BRSET L004D,#$01,L7155 If A/C is On, Go To "Load MPH"
L714F 96 A8 LDAA L00A8 Load Coolant Temperature
L7151 A1 03 CMPA 3,X Compare to Coolant Temperature Low Value Disable
L7153 23 09 BLS L715E Go To "Turn off fan" if Lower
L7155 B6 02 83 L7155 LDAA L0283 Load MPH
L7158 A1 00 CMPA 0,X Compare to High MPH Fan Cutoff
L715A 22 02 BHI L715E Go To "Turn off Fan" if Higher
L715C 20 10 BRA L716E End
L715E 15 52 08 L715E BCLR L0052,#$08 Turn off Fan
L7161 B6 01 51 L7161 LDAA L0151 Load MFR Timer Variable
L7164 D6 02 LDAB L0002 Load Loop Counter
L7166 C4 F0 ANDB #$F0 Mask First 4 Bits
L7168 26 04 BNE L716E Skip To end if no Decrement of Timer Needed
L716A 4A DECA Decrease MFR Timer by 1
L716B B7 01 51 STAA L0151 Save MFR Timer to L0151
L716E 4F L716E CLRA Clear A Register
L716F 5F CLRB Clear B Register
L7170 39 RTS Return


7100: 19 b9 b1 aa 2d 00 00 00 00 00 00 00 00 00 00 00
7110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
7120: ce 71 00 12 52 08 1f 96 a8 a1 01 22 11 12 4d 01
7130: 06 96 a8 a1 02 23 37 b6 02 83 a1 00 22 30 14 52
7140: 08 a6 04 b7 01 51 b6 01 51 26 16 12 4d 01 06 96
7150: a8 a1 03 23 09 b6 02 83 a1 00 22 02 20 10 15 52
7160: 08 b6 01 51 d6 02 c4 f0 26 04 4a b7 01 51 4f 5f
7170: 39