[Lumps!] A/C Diagnois Help Needed

Hello to All,

I posted this strange problem a year or so ago but was never able to find
the answer. It seems to be getting worse. I have an '82 XJ6. I have
Delanair manuals and the shop manual for my car but I haven’t
had any luck in finding the source of this issue.

The issue involves the blowers not ALWAYS sending enough cold air to the
center vents to keep you from sweating on hot days (high humidity days
over 90F degrees). The problem usually occurs during lunchtime

when the car has been sitting out in the sun and the inside temps (with
the windows rolled up are) at least 120F degrees. The blowers work fine in
the morning, and when I first enter the car at lunch they may

work fine. But, if I’m at lunch, and I park the car to run inside a store,
when I crank the car again and put the a/c on high speed, the problem will
most likely surface if the temps outside are 90 and above.

When the problem occurs:

a. Cold air can be felt at the floor vents (by your knees) as normal.

b. If any air at all is coming from the center vents, it’s so minimal that
you’ll still break into a sweat and let the windows down for relief.

c. Raising the hood and shutting it with a slam will sometimes immediately
kick the blowers on and return the system to normal.

d. Pounding once on the top of the dash will sometimes immediately kick
the blowers on and return the system to normal.

e. If you stand outside the car, you can hear air sucking/swirling inside
the small grill in front of the windshield under the wipers. During
normal/correct operation, you can hear no such sucking/swirling at
this grill.

f. sometimes by increasing the engine speed dramatically (e.g., getting on
the interstate) the blowers will work correctly.

g. The cold air sounds as if it’s “trapped” in the center dash and cannot
get out through the vents.

h. Once the blowers have been urged into working correctly, they work
correctly for the remainder of the journey. In other words, they don’t go
in and out…as if there was some loose wire or intermittent fuse
connection.

When the condition occurred, I tried verifying that the Blower Relay
green/slate wire was getting 12v when blower control set to HIGH. I
checked this by gaining access to the blower relay behind the driver’s
kick panel. I used my mulitmeter by setting the dial to “direct current”.
I removed the green/slate wire very, very carefully from the relay with
small needle-nosed pliers. With the a/c running and the blower control set
to HIGH, I touched the red wire of the meter to the terminal where the
green/slate wire had been…while touching the black wire from the meter
to a ground location nearby. The meter read OL, then 12volts. I then
switched the blower control to MED or LOW, tried the same connections and
found that the meter alternated widely amongst values. This seem to prove
to me that the relay seemed to be getting the right signal.

I’ve also pulled and tugged on both a/c related fuses in passenger
fusebox. I’ve also tugged on the wires associated with the a/c relay with
no results.

I’m thinking the problem is related to some split vacuum line, some
unknown (to me) thermostat, or a sticking blower flap.

Any and all suggestions will be appreciated,

Marcus__________________________________________________
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Marcus: from your description, I do not think the problem is in the
blowers. There are two fans; if they are blowing air to the floor, they
are working. The centre event is vacuum controlled; the problem seems to
be there. Either the flap is sticking (and I suspect this because you
say that in high heat conditions the air flow there is blocked; metal
expands with heat, possibly enough to cause a binding; when you slap the
top of the dash, you dislodge the flap), or there is not enough vacuum
to pull the flap open. But a vacuum problem is unlikely to be heat
related. I would pull the centre vent diffuser out of the dash(straight
out) and see if the flap is binding in the high heat conditions you
describe. Once diagnosed, the cure is simple; you need to see where the
binding occurs and lubricate with a touch of grease, or clear the
obstruction.
Gregory-----Original Message-----
From: owner-xj@jag-lovers.org [mailto:owner-xj@jag-lovers.org] On Behalf
Of marcus gentry
Sent: June 14, 2005 7:03 AM
To: Lumps List; jag lovers org
Subject: [xj] A/C Diagnois Help Needed

Hello to All,

I posted this strange problem a year or so ago but was never able to
find
the answer. It seems to be getting worse. I have an '82 XJ6. I have
Delanair manuals and the shop manual for my car but I haven’t
had any luck in finding the source of this issue.

The issue involves the blowers not ALWAYS sending enough cold air to the
center vents to keep you from sweating on hot days (high humidity days
over 90F degrees). The problem usually occurs during lunchtime

when the car has been sitting out in the sun and the inside temps (with
the windows rolled up are) at least 120F degrees.

//please trim quoted text to context only

In reply to a message from marcus gentry sent Tue 14 Jun 2005:

Marcus- Remove the center vent on the dash by puling it out . Check
the metal flap behind it to see if it is opening . Check its
position under both conditions:lots of air and little air. If it is
not opening when little air coming thru,try pushing on it to help
its opening. The vacuum line to the contoller may be cracked or
partially disconnected. or the controller may be sticking. You
can see parts by removing the black dash top. Try driving around
with the center vent and dash top removed and see how things are
working. Bruce–
The original message included these comments:

The issue involves the blowers not ALWAYS sending enough cold air to the
center vents to keep you from sweating on hot days (high humidity days
over 90F degrees). The problem usually occurs during lunchtime
when the car has been sitting out in the sun and the inside temps (with
the windows rolled up are) at least 120F degrees. The blowers work fine in


Bruce Kimball
Columbus/NM, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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// please trim quoted text to context only