A little less AC, please.

[oldertech]

It's the nice time of year where you can drive without A/C here in Kansas, and leanburn is at its best on the highway on the Honda VX, or any other car. As soon as the AC gets kicked in, FE drops.

My idea.... A/C is preset to a certain temp and it cycles on and off based on that preset. Is it adjustable? When I get too cold, my only choice is to either turn off the AC button, or add heat to the system with the temperature control. Inefficient, don't you think?

Assuming that there is no adjustable control somewhere inside the Honda A/C unit on the '92 system, I'm wondering if a secondary A/C thermostat may be installed. (The old underdash A/C units used these switches that had a sensor bulb that read the temp from the evaporator coils and flipped switch contacts on and off.) The adjustable knob could be installed in the dash. It could simply interrupt the signal going to the compressor and turn off the clutch. I could run my AC and decide how warm I want the car for maximum FE.

Thoughts?????

[ShadeTreeMech]

I've often thought about that very thing.

If you were to get a mechanical thermostat for a home AC unit and wire it in to the line that goes from your ac button to the compressor, it should work. the amount of amperage going from the button is usually quite small, and the home thermostats are designed for 24 v DC anyway, so it would be over spec'd for the job at hand. I've never done it myself, but there isn't a reason it wouldn't work that I'm aware of.

Make sure you use a non mercury thermostat, or else you'll be cycling the compressor on and off whenever you turn.

[oldertech]

This is actually the type of unit I was talking about.
http://www.americanpartsdepot.com/im...348%202992.JPG

A mechanical thermostat designed for A/C use that has contacts rated high enough for a compressor clutch.

[ShadeTreeMech]

i doubt the requirements for a compressor clutch are too terribly high. the wires going to the clutch are generally in the 24 guage range, and at 12 v that isn't a high amount of amperage.......

How much is that unit and where did you find it? Is it for a window unit AC?

[comptiger5000]

It's certainly not a bad idea. I think the auto climate control in my Jeep does this to some degree. If I'm stuck in traffic with the A/C on, and it's not hot enough for it to be cranked, I can feel the compressor kick on and off a good bit. I think it still runs it a minimum amount for dehumidifying (for defrost, and cool humid days). It does seem to mix in warmer air as needed, however, to keep the temperature output pretty constant.

[oldertech]

ShadeTreeMech> I just googled thermostat and found that image. It represents what I had in mind. "Universal Air Conditioning" kits have something like it, and after I go to my local auto parts store, I'm betting they have one like it in stock. So I don't know a price. That one was from a website specializing in AMC parts. But the item I have in mind would fit any older car.

[Ryland]

I am pretty sure that the Honda A/C has a relay under the hood, so the wires for the switch are not even running the compressor they are running the relay, so a thermostat would work, check out surpluscenter.com

[brucepick]

Hmm - any thoughts on whether cycling the compressor on/off that much more often would shorten its life?

Any good reason why they got away from the t'stat design? All the older a/c's I've used seemed to have the compressor cycling on/off to keep temperature comfortable. It seems the new ones just stay on and you have to add heat from the engine coolant to get a comfortable temperature.

[Old Mechanic]

I don't use the AC in my 94 VX very much since it really kills the mileage.

I believe the system adjusts the compressor cycling frequency based on temp selection.
You could check to see if the heater control valve is allowing hot water to circulate to the heater core by touching the supply and return hoses to see if hot coolant is actually circulating. On the coldest temp setting I don't think it is circulating.

The way I use my AC is to use the lowest fan setting, max cool and recirculate. If the air is still to cool you can manually cycle the compressor on and off until the air stops coming out of the dash any cooler.

Another way to get the most out of your AC without it costing any fuel, is to cycle the compressor on when you are using DFCO. Since there is no fuel used in DFCO the AC compressor activity is free. Any time you use engine braking, turn the compressor on to cool off the evaporator, then turn it off when you are accelerating or driving at a constant speed. You can leave the fan on until the evaporator has cooled off to the point where the air coming out of the vents is no cooler than the outside air.

Think of it as pulse and gliding the compressor to minimize the energy used to cool the evaporator. The engine idle speed will stay at its normal low setting if the fan speed is less than 2.

More modern cars have seen dramatic changes in the way AC compressors work. Some of them do not even have a clutch anymore. They work by variable displacement in the compressor itself to control pressures in the system, based on demand, and are probably more efficient than you might think.

The systems that mix hot an cold air for climate control usually have a max air setting that can be selected with a low fan speed for best efficiency.

regards
Mech

[brucepick]

Another aspect -
The engine cooling effect of adding engine heat to the a/c'd cabin air can be a good thing if it's running a bit hot.

On my ScanGauge, I've seen this add just enough engine cooling to the system to bring the ECT down into its normal range, when I forgot to remove some grill blocking that wasn't appropriate for the weather.

If you have a digital engine temp gauge (ScanGauge includes one) you can see it happening in detail.