Fan A/C Pressure

[mtnman]

Any ideas on what these should be set at (G0911,G0912)?

What exactly does it affect (I know, "If the A/C pressure is above this value, then turn on fan #1)?

What are the effects if the enable is set very low vs very high?

My fans are (still after many a month) coming on at idle when the AC/Fan is on. I'm wondering if raising the "A/C pressure enable" will keep the fans from coming on until the enable pressure is reached.

[Chevy366]

I think the fans have two properties that are reached , one ECT and the other A/C pressure , so if one or the other is reached the fans come on .
Why would you not want the fans coming on at idle , setting still ?
Under the fuse box cover and outer shroud are the relays that control the fans , you could hook a toggle switch there and toggle the fans if you wanted to , but then again why ?

[mtnman]

I think the fans have two properties that are reached , one ECT and the other A/C pressure , so if one or the other is reached the fans come on .
Why would you not want the fans coming on at idle , setting still ?
When the engine temp is below the setting I have for the fans to come on, the fans will cycle on and off at idle. This cycling happens over and over, on - off, on - off. Fans go off for about 5 seconds then come on 5 seconds. They're coming on when they dont need too as far as the engine temps are concerned. They're coming on cause the A/C compressor is coming on.

I've discussed this 'cycling' problem before with the fans and A/C, but there wasnt really a solution as far as PCM settings go, so I was just wondering what the pressure enable/disable settings were "tied to", wondering if their modification would keep the fans from cycling so much.

[Chevy366]

When the engine temp is below the setting I have for the fans to come on, the fans will cycle on and off at idle. This cycling happens over and over, on - off, on - off. Fans go off for about 5 seconds then come on 5 seconds. They're coming on when they dont need too as far as the engine temps are concerned. They're coming on cause the A/C compressor is coming on.

I've discussed this 'cycling' problem before with the fans and A/C, but there wasnt really a solution as far as PCM settings go, so I was just wondering what the pressure enable/disable settings were "tied to", wondering if their modification would keep the fans from cycling so much.
Your not running a after market fan harness ? , (Nelson) if you are that is your problem right there .
The stock fan harness from GM does not cycle with the A/C as you described .
Here is the stock fan harness part # 15216042 and yes it will fit your 03 .

[mtnman]

Your not running a after market fan harness ? , (Nelson) if you are that is your problem right there .
The stock fan harness from GM does not cycle with the A/C as you described .
Here is the stock fan harness part # 15216042 and yes it will fit your 03 .

Hmm, wish I had known that about 1 year ago. DOH! :bash:

[Chevy366]

Hmm, wish I had known that about 1 year ago. DOH! :bash:
Sorry , but at least you know now , the part number is for the Forward Lamp Assembly Harness which in GM's wisdom contains the fan harness as well .
I just striped out the fan harness stuff and used it , with new convoluted tubing covering the wire that I exposed .

[joecar]

If the enable is set low, then fans will be on always.

If the enable is set high, the A/C can't cause the fans to come on (but ECT can still turn on the fans).

[mtnman]

If the enable is set low, then fans will be on always.

If the enable is set high, the A/C can't cause the fans to come on (but ECT can still turn on the fans).

So, if enable is set high, only the engine temp will be causing the fans to come on? Will this not have adverse affects on the A/C system? Isnt there some correlation between the A/C pressure and the fans?

[Chevy366]

Some PCMs do and some don't depending on year .
You probably only have one trigger wire that one being the one for PIN 42 , on newer PCM's PIN 33 and PIN 42 control the fans for high and low operation as well as the A/C pressure , some people use the PIN 16 for older PCM's .
Without A/C pressure control of the fans the A/C can cause major problems .
I think on ls1tech there is a Pin Out diagram for a 03 PCM might give it a look .

[joecar]

When the A/C compressor comes on, the pressure increases, which would trigger the fans to remove the heat from the condensor coils...

If the fans don't run then the heat isn't removed so you won't get much A/C cooling at low vehicle speeds.

If fans are coming on too easily/often, check:
- is engine overheating...?
- is ECT sensor bad...?
- is A/C overpressurized (I don't know how)...?
- is A/C pressure sensor bad...?
- is there an intermittent short in the fan wiring...?

[Chevy366]

When the A/C compressor comes on, the pressure increases, which would trigger the fans to remove the heat from the condensor coils...

If the fans don't run then the heat isn't removed so you won't get much A/C cooling at low vehicle speeds.

If fans are coming on too easily/often, check:
- is engine overheating...?
- is ECT sensor bad...?
- is A/C overpressurized (I don't know how)...?
- is A/C pressure sensor bad...?
- is there an intermittent short in the fan wiring...?

Joecar everything you say is correct but this is not a stock harness you are dealing with , Nelson Performance sells one that works with LS1 fans but for the larger 05 truck fans it does what he is describing , the harness hooks to the A/C compressor wire in the loom near the engine , thus every time the A/C clutch cycles so do the fans !
Trust me I got rid of one them (Nelson Performance Harness) for this reason , did not like the fans cycling with the A/C clutch .

[joecar]

Joecar everything you say is correct but this is not a stock harness you are dealing with , Nelson Performance sells one that works with LS1 fans but for the larger 05 truck fans it does what he is describing , the harness hooks to the A/C compressor wire in the loom near the engine , thus every time the A/C clutch cycles so do the fans !
Trust me I got rid of one them (Nelson Performance Harness) for this reason , did not like the fans cycling with the A/C clutch .Oh, I see... :doh:

[RonC]

Joecar everything you say is correct but this is not a stock harness you are dealing with , Nelson Performance sells one that works with LS1 fans but for the larger 05 truck fans it does what he is describing , the harness hooks to the A/C compressor wire in the loom near the engine , thus every time the A/C clutch cycles so do the fans !
Trust me I got rid of one them (Nelson Performance Harness) for this reason , did not like the fans cycling with the A/C clutch .

It looks like it can be done on 03 and up to work like the factory fan setup and I have done it on my 05 1500HD using a Modified Nelson harness using pin 33 for high fan and tuning the temp and pressures that I wanted. It has worked just fine for over a year with no problems. See this link for more details;

http://www.performancetrucks.net/forums/showthread.php?t=384964

[mtnman]

It looks like it can be done on 03 and up to work like the factory fan setup and I have done it on my 05 1500HD using a Modified Nelson harness using pin 33 for high fan and tuning the temp and pressures that I wanted. It has worked just fine for over a year with no problems. See this link for more details;

http://www.performancetrucks.net/forums/showthread.php?t=384964

So, are you saying to hook up to pin 33 instead of 42? Or is there more involved? I'm looking at {G0106} in the tune and it's set to "fan #2 control" which seems right according to your ls1 post,"make sure pin 33 is empty and is not used for a/c recirculate".

[RonC]

No, pin 42 is for low speed and pin 33 is for high speed and one is on each big pcm plug. They "ground" to turn on the fans.

[mtnman]

No, pin 42 is for low speed and pin 33 is for high speed and one is on each big pcm plug. They "ground" to turn on the fans.

I've only got pin 42 plugged up. Sorry, but i dont understand what hooking up pin 33 does as far as the fans coming on during A/C cycling. Pin 33 just indicates high fan speed right?

[RonC]

No, pin 42 is for low speed and pin 33 is for high speed and one is on each big pcm plug. They "ground" to turn on the fans.

No, pin 33 turns on and off the high speed fans according to what is setup in the pcm. I think you missed the "grounding" part. The high speed relay has to be wired to "turn on" when it is grounded by pin 33. What harness are you using and how many relays does it have? It might help to reread the post linked above with that thought in mind.

[Chevy366]

For a Nelson Harness to work like the factory one you have to add a relay to the mix , give up on the Nelson piece of junk and get the factory harness , best 180 I've ever spent .
The factory harness comes with relays and fuses , just plug in under the fuse box run to the fans hook up pin 33 and 42 and full control with PCM .
NOTE NELSON HARNESS DOES NOT HAVE FUSES , which can be dangerous.

[RonC]

For a Nelson Harness to work like the factory one you have to add a relay to the mix , give up on the Nelson piece of junk and get the factory harness , best 180 I've ever spent .

Was yours a 2 relay harness. Mine is a Nelson Harness and it works just like the factory does. I had to rewire the high speed relay wires to come on when pin 33 grounded it instead of when the a/c supplied 12V to it. It has to be a 3 relay harnness to work the series - parallel fans though as mine is. I assumed they were all 3 relay. Are they?

[Chevy366]

No 3 relays , added fourth relay for high-low operation to work properly .
Maybe Nelson fixed the problem after me doing a 5 page post on his site about the problem .

[Chevy366]

Say , RonC how do you like the COS3 and SD tune ?
EFILive makes it simple .

[RonC]

I really like it and don't want to go back. I have played with it a lot and have been able to get it where I wanted it. It has been very good and dependable except for the lean startup A00008 problem which they have now fixed. I have got a decent VE table and have setup B3647 for lean cruise on the road and max power when needed. It has been very smooth, runs good, gets 17+ MPG on the road empty and 14+ average driving. Thats around a 2 MPG increase with my old man style driving. I REALLY like EFILive.

[Chevy366]

I really like it and don't want to go back. I have played with it a lot and have been able to get it where I wanted it. It has been very good and dependable except for the lean startup A00008 problem which they have now fixed. I have got a decent VE table and have setup B3647 for lean cruise on the road and max power when needed. It has been very smooth, runs good, gets 17+ MPG on the road empty and 14+ average driving. Thats around a 2 MPG increase with my old man style driving. I REALLY like EFILive.

I have to say DITTO there , I did the COS3 (before fix and re-flashed with fixed), AutoVE and SD and as you said liked the results , I did see a increase in fuel millage as well .
Was just curious if anyone else had the same good results in a HD 6.0L as well.