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A/C compressor info

01xj

NAXJA Forum User
Location
Live Free or Die
I read this on a recent post (from Judd):

"ff....the cycling of the fan when it rains is because you probably
have it on Defrost?? Is supposed to cycle the A/C compressor
and therefore the elec fan. Does a much better job of removing
fog from the windshield using the A/C to help remove moisture
from the air. If not, you do have a water infiltration problem
either under the dash, or really, located at any relay having to
do with the A/C or fan operation."

Does this mean that at every ventilation control setting on the
console (other then the off position) the A/C compressor will
cycle. I've been wondering why I get that cycling sound even
when the A/C is not on. Thought I had a potential problem,
sounds like I don't.

Any experiences with this?
 
Cycling is normal in any A/C mode. It also happens in defrost but should not happen in normal vent or heater modes.

Tom Houston
Loveland, Colorado
 
So the A/C compressor DOES work in some instances when the
A/C is NOT on.

If I have the temperature setting all the way to cold, but do not
have the A/C on, I get the cycling regardless of which ventilation
setting I have selected.

If I move the temp selector to the center (I guess you'd call it
temperature neutral - halfway between cold and hot) - I don't get
the cycling.....

Bizzare ! The OM and the FSM are not very clear on how this
system actually operates.

Maybe I'm picking fly sh__ out of pepper , but in any event - the
cycling is annoying.
 
Never heard of that b 4-

If not in any A/C or defrost mode, the compressor and fan should not be coming on like that. Something is not right somewhere. The cycling it is doing is characteristic to the Defrost setting, so i'd look in that area first. Whatever detrmines that cycle frequency could be it, or something about the actual control is staying in that defrost mode...the switch or related is stuck. Not having come across this before, have to think about this-

As a matter of fact, i love 'manual' things so much (hence the 5-spd and the Warn hubs on my Jeep), that i installed a switch to help control the A/C compressor. In the 'on' position, operates normally. Most the time i find the A/C is not needed when on Defrost. In addition, now the A/C setting can be set on bi-level and only function as vent with the compressor switch 'off'. There is no bi-level in the Vent setting. I also connected a switch to the elec fan so can help to control that too. Works same as the other switch. For that fan to come on with the compressor when cruizing at 70 on the interstate is wasted wear and tear on the system. Kinda anal, but i am usually able to coax an easy 200k miles out of about almost any vehicle with not too many problems....although this Jeep has been a handful at times.
 
Re: Never heard of that b 4-

Judd W. VA said:


As a matter of fact, i love 'manual' things so much (hence the 5-spd and the Warn hubs on my Jeep), that i installed a switch to help control the A/C compressor. In the 'on' position, operates normally.

Interesting. Is this switch simply across the power line to the
compressor? Do you remember the current rating of the switch?
 
Not quite that easy-

It is the PCM that controls the systems overall so did not want to specifically interupt that and/or cause problems with that most complicated and expensive part!! Looking at the FSM wiring diagrams, i found there are two relays associated with those two systems that are always on when the key is on. I simply installed switches cutting off the power to those relays. The PCM thinks the systems are functioning as normal. The switching current for those relays is quite small so any switch can handle that easily.

If you want more specificity i will grab my FSM off the shelf, and provided not many/any changes from my year to your's, i will give you more circuit info.
 
No - I'll sure I'll find it in my FSM, thanks.

Clever switching the relay coils. I'm going to give it a try.

I'd do just about anything to stop the compressor cycling
when all I want to do is circulate ambient air through the
defrost vents - especially on these dry cool New Hampshire
mornings.
 
Yes the A/C compressor will cycles on in any A/C or defrost position (Max, Norm, Mix, and Defrost). I think the easier way to stop it is to interupt the A/C on signal wire from the control head to the PCM.
 
MJR said:
Yes the A/C compressor will cycles on in any A/C or defrost position (Max, Norm, Mix, and Defrost). I think the easier way to stop it is to interupt the A/C on signal wire from the control head to the PCM.

Yes - I'm going to sit down some time this weekend with a couple
of cold ones and just familiarize myself with the entire wiring
system specifically the HVAC system. What "control head" are you
talking about - on the compressor maybe? Do you really think it's
a transparent change to interupt one of the signals to the PCM?
 
01xj said:
What "control head" are you
talking about - on the compressor maybe? Do you really think it's
a transparent change to interupt one of the signals to the PCM?

Yes it is easiest to pull the dash control and put a switch on the A/C input signal.

One should still use caution should this wire be shorted to power (normally switched to ground) it could damage the engine controller
 
almost done......

Ok - I think I've got it figured out.

'01 FSM says the AC control request goes to PCM C3-23.

Can I assume that it dosn't matter if I put a switch (SPST)
before and after the splice to the A/C High Pressure
Switch. I would imagine that switch doesn't engage
until the compressor pressure sends a request to the
PCM for the aux fan.

Now, assuming the A/C high pressure switch is not on,
(because the compressor is not working) can I simply switch
(DPST) the aux fan request to the PCM (C3-13) to ground in
order to turn the aux fan on? It would be great to have a
separate switch to use the aux fan.
 
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