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A/C always ingages in defrost selection??

Odarby

NAXJA Forum User
Location
Seattle
Why does my compressor always ingage when selector is in any of the two defrost selections on my 99 XJ?? Is this normal??
 
Odarby said:
Why does my compressor always ingage when selector is in any of the two defrost selections on my 99 XJ?? Is this normal??

Completely normal - AC systems dehumidify air as they cool it (cold air cannot hold nearly as much water as warm air, so it condenses on the evaporator). This means that the very dry air is blown at the windshield and this helps to quickly pull the water off it.

The AC in my 99 also works. Seems to be the only year without evap problems... :peace:
 
Seems like a waste to me. (Drag on motor/economy) when really not needed. How does it measure ambient temp? Where is the sensor? What would be the best way to make my heater/defroster come on without the a/c cycling? Would I have to add a switch somewhere?
 
I think the "waste" would be minimal, insignificant really. And besides, even on a cool day, you still want dry air on your windshield. Ask me how I know...

But ignoring the "why" and going straight to the "how," you'd just wire a switch in the dash to the wire attached to the top of your compressor. Turn the switch off, the clutch won't engage, and the compressor won't run.

Turn the switch on, and it will cycle normally.

But really, I don't think you "should," even though you "could..."

Two cents...

Robert
 
Thats rediculus - there are times when it can be extremely important to defog a windshield quickly. Why do you think they manufactured it that way?
 
darjevon said:
Thats rediculus - there are times when it can be extremely important to defog a windshield quickly. Why do you think they manufactured it that way?

Hmmmm,...so important that all vehicles have A/C. It is an option. It is the single most power demanding accessory. It is also detrimental for the clearing of ice on the outside of the windshield where heat not cold is the effective factor. It is not rediculus or even ridiculous.
 
Also,compressor engages during defrost-mode to circulate refrigerant WITH compressor- oil thruout the system during the cold months to keep all of the componants well-oiled and corossion-free
 
Odarby said:
It is also detrimental for the clearing of ice on the outside of the windshield where heat not cold is the effective factor. It is not rediculus or even ridiculous.

That is what the Temp knob is for...turn it to the RED side and Voila; you have HOT air!
 
Odarby said:
Hmmmm,...so important that all vehicles have A/C. It is an option. It is the single most power demanding accessory. It is also detrimental for the clearing of ice on the outside of the windshield where heat not cold is the effective factor. It is not rediculus or even ridiculous.
That's when you scrape the windshield while the engine is warming up. Have the controls set to 'Vent' and turn the heat all the way up. That way, when you've got the windshield clear you can jump right back in and drive off. Keeping it on 'Vent' with ocasional forays into 'Defrost' has kept my XJ windshields clear of frost on the inside even during the coldest weather.

Relying on the heater/defroster to clear ice off the outside of the windshield is almost as ridiculous as...disabling the a/c circuit in the defroster.

Jim www.yuccaman.com
 
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