There has to be a wire to the PCM that indicates an A/C on situation form the HVAC controls on the dash. Does anybody know which wire this is? Would it make sense to use it to control turning on and off the E-Fans instead of the compressor switch? This way the fans wouldn't cycle with the compressor, but just stay running when they sense and A/C on signal from the HVAC controls on the dash.
Just wondering if anybody has ever played with this?
No more trucks, but this is what I used to have. 2000 GMC Sierra, 6.0L-LQ4, Built 4L60, LS6 Cam, The Other Guys Headers, 3 inch exhaust and 7 chamber flowmaster, 43lb injectors, Nelson Tuning, Drop - 3/4 McGaughys Spindles, Bell Tech Shackles & Hangers. Best time 13.59 @ 106
That will work. The HVAC signal should be + and constantly on when set to AC. Sorry I don't have a pin out for your truck PCM. I was thinking about setting up a high pressure switch that turns on the fans on the trucks, that way the fans would only run when needed. I have the Camaro setup so my fans already work that way.
2006 Superior Blue Trailblazer SS AWD, Stock as a rock
Sold: 2002 GMC Sportside Denali front end with a 2002 LS1, FLT level 5, Yank 2600, Trick Turbo, T76, Nelson intercooler, 60LB injectors, Warbro fuel pump, Eaton locker, Magnaflow, 3.42, Nelson Performance Tuning (speed density).
Sold: 1981 GMC LB RC 1500 2002 4.8L 4L60E 12 bolt 3.73 Richmond Lock Right AC PS Nelson Performance tuning
High pressure switch? Are you referring to something on the PCM or something external? Right now they come on when the A/C compressor cycles on.Originally posted by GMCwantsLS1@Mar 12 2005, 08:31 AM
That will work. The HVAC signal should be + and constantly on when set to AC. Sorry I don't have a pin out for your truck PCM. I was thinking about setting up a high pressure switch that turns on the fans on the trucks, that way the fans would only run when needed. I have the Camaro setup so my fans already work that way.
No more trucks, but this is what I used to have. 2000 GMC Sierra, 6.0L-LQ4, Built 4L60, LS6 Cam, The Other Guys Headers, 3 inch exhaust and 7 chamber flowmaster, 43lb injectors, Nelson Tuning, Drop - 3/4 McGaughys Spindles, Bell Tech Shackles & Hangers. Best time 13.59 @ 106
Something external, hopefully hooks up to the existing high pressure side fitting. The way it works is like this, when there is no air flow over the condensor, the pressure goes up, this causes the pressure switch to turn on the fans. If you were travleing down the highway, air flow would probally be good enough that the fan would turn off. If the AC is off then low pressure would keep the fan off. It makes the fans work on demand of the system instead of just being on all the time. I had a 1958 truck I added AC 134a system with electric condenser fan and it was set up that way. My buddy Bill with the SS wants to set his up like that too.
Jeff
2006 Superior Blue Trailblazer SS AWD, Stock as a rock
Sold: 2002 GMC Sportside Denali front end with a 2002 LS1, FLT level 5, Yank 2600, Trick Turbo, T76, Nelson intercooler, 60LB injectors, Warbro fuel pump, Eaton locker, Magnaflow, 3.42, Nelson Performance Tuning (speed density).
Sold: 1981 GMC LB RC 1500 2002 4.8L 4L60E 12 bolt 3.73 Richmond Lock Right AC PS Nelson Performance tuning
Thanks for the info! Can the High Pressure Switch from the camaro be adapted to the truck? I'm assuming this would required evacuating the A/C and installing parts and pieces.
No more trucks, but this is what I used to have. 2000 GMC Sierra, 6.0L-LQ4, Built 4L60, LS6 Cam, The Other Guys Headers, 3 inch exhaust and 7 chamber flowmaster, 43lb injectors, Nelson Tuning, Drop - 3/4 McGaughys Spindles, Bell Tech Shackles & Hangers. Best time 13.59 @ 106
Sorry, the one for the Camaro senses presure readings, (transducer type like a gauge and tells the PCM what the actual pressure is) what we need is a switch that closes at a given pressure like 250 PSI. Old Air Products sells one but I'll have to come up with an easy way to tie it into the trucks high pressure line. Also I think other GM's use a pressure switch in this way. I'm trying to avoid the evacuating, recharging thing, it is no problem for me but others I'm sure would like a do-it-yourself setup. I'll keep looking. Ah I came up with a easier way to find AC request. One side of the low pressure switch on your truck's accumulator is AC request and is hot when the HVAC controls are turned on, the other side goes to the compressor relay.
Jeff
2006 Superior Blue Trailblazer SS AWD, Stock as a rock
Sold: 2002 GMC Sportside Denali front end with a 2002 LS1, FLT level 5, Yank 2600, Trick Turbo, T76, Nelson intercooler, 60LB injectors, Warbro fuel pump, Eaton locker, Magnaflow, 3.42, Nelson Performance Tuning (speed density).
Sold: 1981 GMC LB RC 1500 2002 4.8L 4L60E 12 bolt 3.73 Richmond Lock Right AC PS Nelson Performance tuning
So if I understand you correctly, this would keep the fan on as long as there was an A/C request. The fans would not turn on and off when the compressor cycles on and off. This would not do like you suggested earlier and activate the fans based on the pressure . I think it might be a little better, especially when it's cold outside and the A/C is cycling on and off every 10 seconds.
You are a wealth of knowledge! Thanks for the help. Please keep us updated on what you come up with for Bill's SS.
No more trucks, but this is what I used to have. 2000 GMC Sierra, 6.0L-LQ4, Built 4L60, LS6 Cam, The Other Guys Headers, 3 inch exhaust and 7 chamber flowmaster, 43lb injectors, Nelson Tuning, Drop - 3/4 McGaughys Spindles, Bell Tech Shackles & Hangers. Best time 13.59 @ 106
You are correct on all questions! Thank you for the compliment! I'll keep you up to date on Bill's SS.Originally posted by rosscob@Mar 12 2005, 11:54 AM
So if I understand you correctly, this would keep the fan on as long as there was an A/C request. The fans would not turn on and off when the compressor cycles on and off. This would not do like you suggested earlier and activate the fans based on the pressure . I think it might be a little better, especially when it's cold outside and the A/C is cycling on and off every 10 seconds.
You are a wealth of knowledge! Thanks for the help. Please keep us updated on what you come up with for Bill's SS.
2006 Superior Blue Trailblazer SS AWD, Stock as a rock
Sold: 2002 GMC Sportside Denali front end with a 2002 LS1, FLT level 5, Yank 2600, Trick Turbo, T76, Nelson intercooler, 60LB injectors, Warbro fuel pump, Eaton locker, Magnaflow, 3.42, Nelson Performance Tuning (speed density).
Sold: 1981 GMC LB RC 1500 2002 4.8L 4L60E 12 bolt 3.73 Richmond Lock Right AC PS Nelson Performance tuning
I'm not sure if you said this already, but what kind of measurement/reading does the current sensor put out? Does the resistance or voltage go up as the pressure goes up?
Could we just tap into the high pressure switch wire that is currently on there and have it trigger a relay?
I like the idea of having the fan come on only when the pressure exceeds a certain limit, that way the clutch can cycle as much as it wants and not trigger the fan.
back to the drawing boards on the harness, lol.
thanks,
allen
Nelson Performance
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Replace the stock low pressure A/C cutoff switch with an high pressure switch? Jumper the low pressure override. Run the a/c relay ground through the high pressure switch and then to ground?
See my truck data in the "My Garage" section here... http://www.ls1truck.com/forums/my-ga...tml#post191709
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