A/C Compressor is always on?

[SoNic67]

And WHAT causes the LOW side pressure value? Heat.
On manual A/C, will be determined by the amount of heat that you will extract from the car, via evaporator coil. That is based on the delta temperature.
More extracted heat (lower cooling setting inside compared to outside temperature) means bigger delta T, will drop the pressure more, forcing the compressor to run longer to re-create from that LOW back the HIGH pressure.
Is not the same work to go from 30 to 220 psi as from 60 to 220 psi.
On automatic A/C, the red button or settings on dial creates a set-point for inside temperature. When that is achieved, the compressor is turned off. When temperature raises past the upper limit, compressor is on. How often depends of the heat resistance of your car and delta T. Bigger delta T (for a given car thermal insulation) will make compressor work longer.

Lower pressure side switch will cut-off the compressor when pressure drops very low. Like when is not enough refrigerant. A/C pressure testing gauges are cheap.

 

[exploration1997]

1. about 10 secs on and 5 secs off doesn't sound like it needs any refrigerant to me. my '01 EB cycles about that often and it will freeze you out of the truck. it's the coldest a/c I've ever owned.

2. I don't believe that setting the TEMP knob nearer the red side has any effect on how often the compressor kicks in (or how long it runs). if the a/c is on, it's on. what causes the compressor to cycle is the HIGH pressure switch. this (pressure) in turn is effected by ambient outside temperature. setting the TEMP knob near/in the red just adds heater air so the a/c isn't as cold. if your truck has EATC, setting the automatic TEMP setting higher does the same thing.

Oh okay thanks. You seem to be pretty knowledgable about this stuff. So if down the road I want to convert to EATC, would you mind giving me a few pointers?

 

[exploration1997]

And WHAT causes the LOW side pressure value? Heat.
On manual A/C, will be determined by the amount of heat that you will extract from the car, via evaporator coil. That is based on the delta temperature.
More extracted heat (lower cooling setting inside compared to outside temperature) means bigger delta T, will drop the pressure more, forcing the compressor to run longer to re-create from that LOW back the HIGH pressure.
Is not the same work to go from 30 to 210 psi as from 60 to 210 psi.
On automatic A/C, the red button or settings on dial creates a set-point for inside temperature. When that is achieved, the compressor is turned off. When temperature raises past the upper limit, compressor is on. How often depends of the heat resistance of your car and delta T. Bigger delta T (for a given car thermal insulation) will make compressor work longer.

Oh, ok thanks. I don't exactly know what point you're trying to get across, but it's information, so thanks.

 

[SoNic67]

My point: Extra gas consumption due to A/C is based on the temperature setting. The bigger the difference between outside and inside, bigger will be the added gas 'cost'.
Actually is the same in your house too, just that the extra cost is due to electricity cost.

If you don't want the A/C compressor to start, use the VENT position (or FEET ONLY), like is described in the owner manual.

If you need A/C but want to save gas too, use the 'Max A/C' position (no hot outside air) and lower the fan speed till you get the desired temperature inside the car (minimize the heat extraction on lowest fan speed setting).

 

[koda2000]

Oh okay thanks. You seem to be pretty knowledgable about this stuff. So if down the road I want to convert to EATC, would you mind giving me a few pointers?

i'd be happy to share what I know, but I've never done a conversion to EATC. I recall someone on the forum asking about doing it once, and someone telling him it could be done fairly easily (try searching previous posts). I know the blower resistor has to be replaced with an electronic blower module and, of course, the manual HVAC controls get replaced. I imagine the biggest issue would be changing over the wiring and, to a lesser degree, the vacuum lines. the EATC control module can be problematic (small o-rings and solenoids) so grabbing one the salvage yard is a crap shoot. reman units, or rebuilding, runs around $100. all my current trucks have the EATC's, but I'm rather indifferent to it. it looks cool, but when I want cool I always run it at 60 and when I want heat it's usually set for around 80. I never really blend, but women seem to like the ability to do so.

 

[bill06447]

Well, I can say my 97 XLT 5.0 AWD with manual AC only kicks the compressor on in AC, MAX, defrost and defrost blend positions. Guessing there's an issue with the blend selector.

Bill