Vacuum operated switch to control A/C compressor?
02-19-2011, 09:46 AM
#1
Vacuum operated switch to control A/C compressor? I was thinking about installing some sort of vacuum operated switch inline with my A/C compressor clutch wire. When the car has a healthy amount of vacuum, the switch will be closed and the A/C compressor will be allowed to come on whenever my climate control requests it. When the car has very weak vacuum or zero vacuum, the switch would be open, which would prevent the compressor from turning on.
Under normal driving and idling, the compressor would be allowed to come on because the vacuum would be high. Under WOT and while starting the car, vacuum would be very weak or zero, and the A/C compressor would not be allowed to come on.
Has anyone every tried this before? Think it'll work properly?
Where can I find a decent vacuum operated electrical switch? I took a look at the "Hobbs" switch and I am not a big fan of the exposed connectors or the screw-in vacuum port design. It seems like they're for boost anyway, and not vacuum. I don't know what pressure/vacuum I would switch at (10 in HG?) so I will probably need to get a vacuum gauge and see where my vacuum is at WOT... then find a switch that falls within that range, or get an adjustable switch.
Any input would be helpful!
(I am running a later truck PCM that receives the A/C request signal from the heater controls over the serial data lines, rather than just getting a +12v signal over the A/C request wire. As a result, I can't use the PCM to turn the compressor on and off. I am also running DBW, so I can't really put a switch on the throttle body. I could put one on the gas pedal, but I think the vacuum switch would be simpler/easier/cooler.)
Under normal driving and idling, the compressor would be allowed to come on because the vacuum would be high. Under WOT and while starting the car, vacuum would be very weak or zero, and the A/C compressor would not be allowed to come on.
Has anyone every tried this before? Think it'll work properly?
Where can I find a decent vacuum operated electrical switch? I took a look at the "Hobbs" switch and I am not a big fan of the exposed connectors or the screw-in vacuum port design. It seems like they're for boost anyway, and not vacuum. I don't know what pressure/vacuum I would switch at (10 in HG?) so I will probably need to get a vacuum gauge and see where my vacuum is at WOT... then find a switch that falls within that range, or get an adjustable switch.
Any input would be helpful!
(I am running a later truck PCM that receives the A/C request signal from the heater controls over the serial data lines, rather than just getting a +12v signal over the A/C request wire. As a result, I can't use the PCM to turn the compressor on and off. I am also running DBW, so I can't really put a switch on the throttle body. I could put one on the gas pedal, but I think the vacuum switch would be simpler/easier/cooler.)
02-21-2011, 01:32 PM
#3
I can't believe nobody's tried this before, or has any interest?!
Yea, 5 HP doesn't sound like all that much... I guess it's really not. I did read that the F-body A/C compressors don't particularly like high RPMs either, which is where a lot of your WOT activity is going to occur. Maybe this is part of the reason the PCM disables the A/C compressor clutch at WOT?
A switch is definitely an idea, but I'd rather make it do it automatically. I don't want to be looking down for a switch every time I want to pass/kill a car on the highway - things happen too fast on our roads!
I really want to try this out. Are there any options besides the Honeywell/Hobbs switches? I found ones that are vacuum-operated rather than pressure operated, but I would like a couple other options as well. Anybody know where I can get a vacuum operated electrical switch?
Yea, 5 HP doesn't sound like all that much... I guess it's really not. I did read that the F-body A/C compressors don't particularly like high RPMs either, which is where a lot of your WOT activity is going to occur. Maybe this is part of the reason the PCM disables the A/C compressor clutch at WOT?
A switch is definitely an idea, but I'd rather make it do it automatically. I don't want to be looking down for a switch every time I want to pass/kill a car on the highway - things happen too fast on our roads!
I really want to try this out. Are there any options besides the Honeywell/Hobbs switches? I found ones that are vacuum-operated rather than pressure operated, but I would like a couple other options as well. Anybody know where I can get a vacuum operated electrical switch?
Last edited by FastKat; 02-21-2011 at 01:38 PM.
02-22-2011, 09:56 PM
#5
Ahh, I forgot about McMaster Carr. Those switches are expensive!
Here is what I was looking at from Honeywell, and probably what I will wind up using - it's on the 4th (last) page. It is a Hobbs-style switch, but at least they offer a cover for the terminals.
http://content.honeywell.com/sensing...scorp/P3_6.pdf
I'll have to determine the appropriate vacuum with a vacuum gauge before I order the switch. I was hoping there were some OEM vacuum switches out there, but I guess not.
Here is what I was looking at from Honeywell, and probably what I will wind up using - it's on the 4th (last) page. It is a Hobbs-style switch, but at least they offer a cover for the terminals.
http://content.honeywell.com/sensing...scorp/P3_6.pdf
I'll have to determine the appropriate vacuum with a vacuum gauge before I order the switch. I was hoping there were some OEM vacuum switches out there, but I guess not.
