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2nd Gen Non-Engine/Transmission A/C compressor on-off

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Maybe a little boring question, but how exactly does the A/C compressor cycle... or whats normal. Mine seems to kick on and off occasionally even when I'm not using heat or A/C.



I understand that sometimes they kick on when the defrost is on, but is that also true when the temp switch is turned to "hot" with the defrost on? Seems like it should not kick on unless the AC is on to me. The only other vehicle I've owned with A/C was a 97 GMC Z-71 and I didn't notice this situation (of course a totally different brand). If its normal for a Dodge, thats fine as long as I am aware of it. Thanks... :)
 
It's normal.......

There are only two settings I believe that don't cycle the compressor for AC on demand. I don't particularly like the way it operates either.



Someone did have a thread going with pictures of adding a switch to turn the AC on and off. That way you could run the settings you wanted without cycling the compressor.



Can't remember the name but it should show up in a search.



Garrett
 
Thanks, I'll look into this as I really hate how I run my defrost in the summer time when its raining and fog still ends up on the windshield cause the AC is running causing way too cool air to hit the glass
 
That may make it worse...

Neil, the A/C actually makes the defroster work better as it removes moisture from the air being blown up to the defrost vents. This is the reason for the compressor wired to run in the defrost mode.



Sam
 
During defog mode in hot weather, thats fine with me... but what about when the temp control is all the way over in the red. Seems kinda strange that the temp control is all the way over in the "RED" zone (hot) and the AC is kicking on when I'm trying to get frost off the windshield. Maybe its programmed to run AC no matter what the temp is set at during "defog or defrost" operation.
 
Originally posted by Ncostello

During defog mode in hot weather, thats fine with me... but what about when the temp control is all the way over in the red. Seems kinda strange that the temp control is all the way over in the "RED" zone (hot) and the AC is kicking on when I'm trying to get frost off the windshield.



This is known in the heating, ventilation and air conditioning trade as chilled air with reheat. The air is chilled to condense out the moisture. It is then reheated to the desired temperature you've set on your temperature control dial. The compressor is working just the way it was designed to do.



If it weren't running this way, you wouldn't like the results when the warm air hit a cold windshield - the windshield would condense out the moisture in the air coming from the defroster outlets, and you'd be building condensation on the inside of the windshield while you're trying to melt ice, snow or frost from the outside of the windshield.



Rusty
 
Cool... . no pun intended!:) Thanks for the info. I wont worry about it now. I do need to extend my evap drain tube a little though. I dont like how it runs all over the firewall then down the frame rail. Could get into bad places and start rust.
 
Ncostello



You 97 GM truck probably had a variable displacement compressor and your Dodge has a conventional fixed displacement compressor. Both trucks have what's called and "orifice tube" to control how much refrigerant goes into the evaporator to do the cooling/dehumidifying. Both rigs run the compressor in defrost as RustyJC stated.



This means:

The the orifice tube lets "X" amount of refrigerant through, the tube can't regulate the amount, unlike a Thermal Expansion Valve found on most Mopar cars. This could allow the evaporator to become too cold and the moisture from the ambient air would freeze on the fins and restrict the air flow that the blower motor is moving.



To prevent freeze up, the fixed displacement system must turn the compressor "on and off" to maintain the temp of the evaporator just above freezing; the variable displacement compressor can vary it's output to help keep the evaporator temp correct, so we don't need to cycle the compressor very much (if at all), so no clicking on and off.



Mopar has run some variable displacement stuff on Town and Country minivans and some early 90's Imperials, that's all I'm aware of there's probably more.



Wayne
 
Another positive for the compressor to run with the heat/defrost is it keeps the seals lubricated and the oil circulated thoughout the a/c system during the winter months. ;)
 
Ncostello,



When ever you use the mix settings on your heater Floor/vent or floor/def, the compressor is working. So when there is a lot of condensation, they are great to use as described above. But after your vehicle is warmed up and you have control of the moisture, you want to change the mixed controls to a single control, vent, defrost, or floor. This stops the condenser from working overtime and if you have the temp control turned to the coldest setting, the air conditioner is working through the cold time of the year.



Blair
 
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