Defrost requires the AC compressor ...?

So I'm parking the XJ today after driving home, and as I get out I
notice that the aux cooling fan is still spinning (Ignition off, key
out). It's been raining, so it hasn't been whatcha might call "warm"
out. Well, I have a motorcycle that does this sometimes, and I've only
had the Jeep since October, so I decide to check it again later.

Twenty minutes later and the fan's still going ...!?!
(The engine is very much on the cold side by this time.)
I unplug it and go back inside and google this group and discover its
not uncommon for this to happen.

I go back outside and fiddle (sorry for the tech speak) with the
relay, and move the control OFF of the Defrost setting and lo and
behold the fan doesn't spin after I plug it back in. Chalk up another
repair to "hitting it with a bigger hammer". (Someone remind me to ask
my mechanic about this later.Thanks.)

So, anyway, to get to the point (what was my point again?...oh yeah),
while reading past posts on the issue, I read several posts that
stated that the AC compressor is activated when you use the Defroster.

....?wtf?...

Please, someone explain. This doesn't seem to make sense.

TIA

(95 XJ Sport, 4.0L Auto)

....

The a/c is turned on by selecting the defrost position. The electric
fan is turned on by the A/C relay. That means the fan is indirectly
powered up by the defroster (a/c dries the defrost air to make it work
better). BOTH the a/c and the high temp switch on the radiator
trigger the fan thru a relay and both are switched power thru the
ignition switch, so if the fan keeps running with the ignition off you
have some sort of electrical problem - possibly a stuck fan relay.
You don't give a model year, but on the 86-90 XJ, the fan relay is on
the driver's side fender next to the air cleaner. I'm not sure about
the location on later models. If you go back tomorrow and plug the
fan back in and it starts right off, pull the relay. That should shut
it off and indicate a stuck relay. Replacement relays are cheap -
just get a new one and plug it in IF that seems to be the problem.

On Wed, 5 Apr 2006 05:00:46 UTC noneyabusiness > wrote:

> So I'm parking the XJ today after driving home, and as I get out I
> notice that the aux cooling fan is still spinning (Ignition off, key
> out). It's been raining, so it hasn't been whatcha might call "warm"
> out. Well, I have a motorcycle that does this sometimes, and I've only
> had the Jeep since October, so I decide to check it again later.
>
> Twenty minutes later and the fan's still going ...!?!
> (The engine is very much on the cold side by this time.)
> I unplug it and go back inside and google this group and discover its
> not uncommon for this to happen.
>
> I go back outside and fiddle (sorry for the tech speak) with the
> relay, and move the control OFF of the Defrost setting and lo and
> behold the fan doesn't spin after I plug it back in. Chalk up another
> repair to "hitting it with a bigger hammer". (Someone remind me to ask
> my mechanic about this later.Thanks.)
>
> So, anyway, to get to the point (what was my point again?...oh yeah),
> while reading past posts on the issue, I read several posts that
> stated that the AC compressor is activated when you use the Defroster.
>
> ...?wtf?...
>
> Please, someone explain. This doesn't seem to make sense.
>
> TIA
>
> (95 XJ Sport, 4.0L Auto)
>
> ...


--
Will Honea

noneyabusiness wrote:
-snip-
> So, anyway, to get to the point (what was my point again?...oh yeah),
> while reading past posts on the issue, I read several posts that
> stated that the AC compressor is activated when you use the Defroster.
>
> ...?wtf?...
>
> Please, someone explain. This doesn't seem to make sense.
>
> TIA
>
> (95 XJ Sport, 4.0L Auto)

Usually the case. The fan control on my Cherokee shows the defrost
setting as being an A/C setting. It's normal practice, since using
the A/C in defrost mode will clear a windscreen in seconds, due to the
difference in humidity of the incoming (conditioned) air. Merely
putting the heater on will usually result in a wet and warm windscreen
that takes longer to clear. A/C can be used in any heat position, I
believe.

It's a bit of a circular argument though, since when the A/C is off
(on cars I'ved owned) the incoming air seems damper, so mists up more
readily, requiring the A/C to quickly clear it...


--
Regards,
Danny

http://www.gaggia-espresso.com (a purely hobby site)
http://www.dannyscoffee.com (UK advert for my mobile espresso service)
http://www.malabargold.co.uk (UK/European online ordering for Malabar
Gold blend)
swap Z for above characters in email address to reply

I don't know a thing about your problem, but I got a good laugh out of your
post!
Kate

"noneyabusiness" > wrote in message
...
: So I'm parking the XJ today after driving home, and as I get out I
: notice that the aux cooling fan is still spinning (Ignition off, key
: out). It's been raining, so it hasn't been whatcha might call "warm"
: out. Well, I have a motorcycle that does this sometimes, and I've only
: had the Jeep since October, so I decide to check it again later.
:
: Twenty minutes later and the fan's still going ...!?!
: (The engine is very much on the cold side by this time.)
: I unplug it and go back inside and google this group and discover its
: not uncommon for this to happen.
:
: I go back outside and fiddle (sorry for the tech speak) with the
: relay, and move the control OFF of the Defrost setting and lo and
: behold the fan doesn't spin after I plug it back in. Chalk up another
: repair to "hitting it with a bigger hammer". (Someone remind me to ask
: my mechanic about this later.Thanks.)
:
: So, anyway, to get to the point (what was my point again?...oh yeah),
: while reading past posts on the issue, I read several posts that
: stated that the AC compressor is activated when you use the Defroster.
:
: ...?wtf?...
:
: Please, someone explain. This doesn't seem to make sense.
:
: TIA
:
: (95 XJ Sport, 4.0L Auto)
:
: ...

On Wed, 5 Apr 2006 02:49:13 -0400, "billy ray"
> wrote:

>Passing the cabin air over cooling coils dehumidifies the air then it passes
>over the heating coils.
>

AH!! NOW it makes sense!
Thanks a bunch (to you AND the others who replied)!

....

>
>"noneyabusiness" > wrote in message
.. .
>> So I'm parking the XJ today after driving home, and as I get out I
>> notice that the aux cooling fan is still spinning (Ignition off, key
>> out). It's been raining, so it hasn't been whatcha might call "warm"
>> out. Well, I have a motorcycle that does this sometimes, and I've only
>> had the Jeep since October, so I decide to check it again later.
>>
>> Twenty minutes later and the fan's still going ...!?!
>> (The engine is very much on the cold side by this time.)
>> I unplug it and go back inside and google this group and discover its
>> not uncommon for this to happen.
>>
>> I go back outside and fiddle (sorry for the tech speak) with the
>> relay, and move the control OFF of the Defrost setting and lo and
>> behold the fan doesn't spin after I plug it back in. Chalk up another
>> repair to "hitting it with a bigger hammer". (Someone remind me to ask
>> my mechanic about this later.Thanks.)
>>
>> So, anyway, to get to the point (what was my point again?...oh yeah),
>> while reading past posts on the issue, I read several posts that
>> stated that the AC compressor is activated when you use the Defroster.
>>
>> ...?wtf?...
>>
>> Please, someone explain. This doesn't seem to make sense.
>>
>> TIA
>>
>> (95 XJ Sport, 4.0L Auto)
>>
>> ...
>

"noneyabusiness" > wrote in message
...
> So I'm parking the XJ today after driving home, and as I get out I
> notice that the aux cooling fan is still spinning (Ignition off, key
> out). It's been raining, so it hasn't been whatcha might call "warm"
> out. Well, I have a motorcycle that does this sometimes, and I've only
> had the Jeep since October, so I decide to check it again later.
>
> Twenty minutes later and the fan's still going ...!?!
> (The engine is very much on the cold side by this time.)
> I unplug it and go back inside and google this group and discover its
> not uncommon for this to happen.
>
> I go back outside and fiddle (sorry for the tech speak) with the
> relay, and move the control OFF of the Defrost setting and lo and
> behold the fan doesn't spin after I plug it back in. Chalk up another
> repair to "hitting it with a bigger hammer". (Someone remind me to ask
> my mechanic about this later.Thanks.)
>


Don't bother your mechanic with this one. The AC runs with the defroster
because the AC is really a dehumidifier. The fog on the inside of the
windshield is humidity, the AC is a dehumidifier. See the connection?