Brian Nystrom

I'm not sure if you'll even want to answer this, but here goes.

I really dislike the fact that the A/C in my '04 Elantra is coupled to
the defroster so that the they always come on together. I've heard a
rumor that this is a new federally mandated setup, but frankly, it
really sucks if you live in a cold environment and need maximum heat to
clear snow and ice from the windshield. On '03 and older cars, it's a
simple matter of snipping one signal wire to decouple them, but still be
able to turn on the A/C manually with the defroster if you want to.

Unfortunately, he '04 has a different control module that's more
difficult to decipher. I've examined the wiring diagrams, but it's hard
to relate them to the components. I'm on the verge of opening the
control module in the dash to see if I can find where the signal from
the mode selector switch connects to the the A/C signal output, so I can
sever the connection. Any ideas?

hyundaitech

The climate control head communicates a/c compressor request directly to
the PCM, and they don't specify the nature of the signal. I'd be tempted
to put a switch inside the vehicle in-line between the a/c relay and the
compressor. That way, you'd be able to reenergize the compressor when you
wished.

Richard Steinfeld

"Brian Nystrom" <brian.nystrom@att.net> wrote in message
news:8wV0e.454367$w62.371477@bgtnsc05-news.ops.worldnet.att.net...
| I'm not sure if you'll even want to answer this, but here goes.
|
| I really dislike the fact that the A/C in my '04 Elantra is
coupled to
| the defroster so that the they always come on together. I've
heard a
| rumor that this is a new federally mandated setup, but frankly,
it
| really sucks if you live in a cold environment and need maximum
heat to
| clear snow and ice from the windshield. On '03 and older cars,
it's a
| simple matter of snipping one signal wire to decouple them, but
still be
| able to turn on the A/C manually with the defroster if you want
to.

I agree with you. This was one on the list of engineering
stupidities of my late Ford Aerostar, which has met its just
reward after passing through purgatory. This design sticks in my
craw (and I don't even know what a "craw" is). And I don't even
live in a cold climate. My 2000 Sonata's heat comes up nice and
quick, but if I lived where it's cold, I'd want a whole lot
quicker.

The other thing that gets me is that carmakers have been making
"always-on" heater cores, with the output controlled only by a
big air flap. In my experience, these tend to leak hot air into
the interior on a hot day. I'm not certain that my Sonata is set
up this way -- I haven't owned the car long enough to
investigate. It's an old practice, though: it was a "feature" of
my 66 Plymouth. I can't understand why they didn't use the
old-time idea of just putting a water valve in the hot water
line. These flap air deflectors leak in two ways, often both at
once:
- They radiate from the heater housing, which is usually black to
help transmit the heat.
- The flaps often don't seal very well, either due to internal
leakage past the flap, or from wear in the vacuum activators, or
even perhaps a little vacuum leak in the tubing or controls.
The result is sometimes hot air blown on your face whenever you
want heat on your toes.

So, I've often wondered about the practicality of just putting a
water valve in one of the heater hoses to shut off the heat
totally in the summer. Or, is there some reason why the engine or
emissions will be harmed if the coolant isn't circulated through
the heater at all thimes?

Richard

hyundaitech

My experience is that the problems with the water valves tend to be worse
than the side-effects of an always on heater core. The water valves bind,
or worse, leak sometimes. Having experienced it both ways in my cars, I'll
take the always on heater core.

There's actually a good reason the automakers turn on the a/c for defrost.
It dehumidifies the air and defogs the windows much more quickly. But, I
can also see the desire to have it not energized if you're still getting
cold air.

Richard Steinfeld

"hyundaitech" <notpublic@not.public.com> wrote in message
news:7a0d3df395b86d80e351e5d23dc87138@localhost.ta lkaboutautos.com...
| My experience is that the problems with the water valves tend
to be worse
| than the side-effects of an always on heater core. The water
valves bind,
| or worse, leak sometimes. Having experienced it both ways in
my cars, I'll
| take the always on heater core.
|
| There's actually a good reason the automakers turn on the a/c
for defrost.
| It dehumidifies the air and defogs the windows much more
quickly. But, I
| can also see the desire to have it not energized if you're
still getting
| cold air.
|
Thanks. I sit corrected. I wonder if the valve problems may have
something to do with mineral content in the water -- I've never
experienced this problem in my life, but I've never lived where
the water was very hard. I understand about the defrost a/c.
There's a hidden comfort advantage that I've found with this:
running the defroster in the summer is a nice way to get diffused
cold air from the air conditioner, rather than the usual blast in
the face. Try it, you'll like it.

Richard

Brian Nystrom

hyundaitech wrote:
> The climate control head communicates a/c compressor request directly to
> the PCM, and they don't specify the nature of the signal. I'd be tempted
> to put a switch inside the vehicle in-line between the a/c relay and the
> compressor. That way, you'd be able to reenergize the compressor when you
> wished.

Thanks for the pointers.

Functionally, that's what I want to do. I'm thinking that I may be able
to use the existing switch by carefully re-routing the wiring.
Essentially, I would have the a/c signal on all the time between the
control head and PCM (bypassing the existing switch), but put the switch
in the signal line to the relay or between the relay and compressor as
you suggest (if it will handle the current load). That would maintain
the stock appearance and intuitive functionality. Thoughts?

Brian Nystrom

hyundaitech wrote:
> My experience is that the problems with the water valves tend to be worse
> than the side-effects of an always on heater core. The water valves bind,
> or worse, leak sometimes. Having experienced it both ways in my cars, I'll
> take the always on heater core.

I've had leaky heater valves and they're not fun to deal with.

> There's actually a good reason the automakers turn on the a/c for defrost.
> It dehumidifies the air and defogs the windows much more quickly. But, I
> can also see the desire to have it not energized if you're still getting
> cold air.

Having dry air can be critical to de-FOGGING the INSIDE of the
windshield. Where I have an issue is when I'm trying to de-FROST the
OUTSIDE of the windshield. The reduced air temp from having the A/C
compressor running reduces the efficiency of the defogger/defroster in
clearing snow and ice. I had a problem with this on one particularly
nasty trip this winter and I'm going to do something about it before it
gets me killed.

BTW, I understand that Canadian market Hyundais do not have the a/c and
defroster coupled permanently. When you turn on the defroster, the a/c
turns on (and the switch lights up), but you can manually turn it off.
That's a good solution and what we should have here, IMO. Unfortunately,
it appears that the parts are not interchangeable.

Gnekker

> There's actually a good reason the automakers turn on the a/c for defrost.
> It dehumidifies the air and defogs the windows much more quickly. But, I
> can also see the desire to have it not energized if you're still getting
> cold air.

There is a catch, also. That way, water taken from the air is trapped
on the evaporator, and quickly released back into air stream if you
turn off a/c. So if you defrost with a/c, you have to keep it on. And
I don't like to drive around in winter time with a/c running. Or
better said, I don't like to use it at all untill the heat is
unbearable.

S25

On Fri, 25 Mar 2005 14:47:32 GMT, Brian Nystrom
<brian.nystrom@att.net> wrote:

>I'm not sure if you'll even want to answer this, but here goes.
>
>I really dislike the fact that the A/C in my '04 Elantra is coupled to
>the defroster so that the they always come on together. I've heard a
>rumor that this is a new federally mandated setup, but frankly, it
>really sucks if you live in a cold environment and need maximum heat to
>clear snow and ice from the windshield. On '03 and older cars, it's a
>simple matter of snipping one signal wire to decouple them, but still be
>able to turn on the A/C manually with the defroster if you want to.
> <snip>
====================

In my 'old' cars, the a/c systems had ambient temp sensors (about
36-38 degrees F.) that killed the power to the a/c compressor clutch
when the temp was low. Doesn't do the compressor any good to pump
into a frozen system. Have you actually looked at the compressor to
see if it runs? Or are you just looking at the dash light?

I'd check on my Santa Fe, but I live in Florida and ... =;-)

S25