checking Air Conditioner

frankb_cAugust 2, 2005

Grand Marquis 2000 Mercury. 4.6 L V8

The A/C is blasting out Hot air now.Worked fine till yesterday.

Do not get that clicking sound of the compressor switching On/off.

My mechanic on holidays till next monday.

How can I check?

Is this a sensor gone?

Any Ideas would be appreciated.

You bet I'll be at their doorstep Monday AM Early.

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if it stopped in a 24 hour period as you say it is probably
electrical. Unless an A.C. hose ripped off when you hit a
bump i'd go that route. A lot of the newer cars, and yours
is one of them, the A.C. is computer controled by the B.C.M. As much as a 3 oz. charge difference will lock it off. It is now tuesday. What did your guy say ?

    Bookmark   August 2, 2005 at 6:02PM
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Garage on holidays till Aug.8th.
What is B.C.M.?
3 oz. charge / Electrical? Lock it off?
Is there a reset method, I could perform?
Temp today is 90+ degrees.

Tools, and time I got. Used to change my own spark plugs,change oil, grease, body work, tires,in my younger days.
Even dropped a differential on an "Anglia" (Ford,English 1951) to change to pin. My first car.

    Bookmark   August 3, 2005 at 1:49PM
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Probably ran out of the 134a "freon", this seems to stay around for 5 to 7 years - seems to be normal now-a-days; 134a has a tendenacy to seep..
When too low a charge is detected, the compressor will not run..

I hate acronyms - people should NOT use these so freely and easily !
BCM = body control module ?? A Chrysler term, may not be a GM or VW term.

    Bookmark   August 3, 2005 at 2:42PM
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Thank you earthworm.
Body control Module? what is that?
On board computer?
Car is made by FORD.

    Bookmark   August 3, 2005 at 7:21PM
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The body control module is, to the best of my knowledge, a simple on-board computer. You need a refill of refrigerant,Frank.


BCM is TTBOMK is a OBC. HVAC service due, Frank.

    Bookmark   August 4, 2005 at 12:17PM
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Yes, most cars today have two computers (at least). The PCM is the powertrain control module, which controls the engine functions, and the BCM, body control module, which controls accessories such as heating and a/c, and increasingly it even watches over things like power locks, power windows, interior lights, etc. This is what gives functions like "retained accessory power," where the radio and other stuff keeps running for a while after you shut the car off (until you open the front door), and "battery rundown protection," which will shut off interior or exterior lights after a period of time if they're accidentally left on.

When you turn on the a/c, that doesn't directly trigger a switch in the a/c system. Instead, you are putting in a request to the BCM, and if various conditions are met, such as engine not being overheated, RPM not above a certain level, etc., the BCM will in turn start the a/c compressor.

But all of this is pretty irrelevant to the average car owner like you and me, because if these modules are bad, there isn't much we can do about it. The good thing is, however, that they very rarely fail. Most likely you BCM is working right, and some condition that it's checking for in the a/c is not being met, such as it might have insufficient refrigerant, or maybe there is a sensor that's bad which is giving the BCM faulty data. Bottom line is, you really need to take it to someone who can test it and see what's going on.

    Bookmark   August 4, 2005 at 1:43PM
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Thanks, Monday id not that far off.

    Bookmark   August 4, 2005 at 1:52PM
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If you do just go in and need a simple service (not sure if that is possible through your tech with a possible leak in the system), but let us know the before service pressures and the after service pressures. If you still are looking for help then we will need the beginning pressures please to continue, this is universally required info on an AC question. These will be the HI (compressor output) and the LO (compressor return, after it has cooled your car).

Duane in Japan

    Bookmark   August 5, 2005 at 11:41AM
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After all the waiting. Mechanic was quick to say freon is low.
But only 6 oz. That should not stop A/C from working. Further testing proved out his statement. A connection "block" of wires on the drivers side in Engine compartment showed that that the connectors had some corrosion. once he bypassed this, the clutch kicked in. After a little bypass surgery, this will not be a repeated. Still, Drained and re-tested pressure, re-filled to full.
Repair on the cheap. Worth the wait.

High today 32c, but in car a cool 69 degrees.
Amen. Thanks to all for your support.

    Bookmark   August 9, 2005 at 10:06AM
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