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1989 Cadillac Sedan DeVille, 1992 Cadillac Sedan DeVille
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28 Posts
Discussion Starter #1
My A/C on my 92 Deville was recently charged and cools to 38 degrees coming out of the upper vents. However, I only have two speeds when I use to have five speeds. The "Low Fan" still works the same, but the other four speeds, "Low Auto Fan", "Auto Fan", "High Auto Fan" and "High Fan" all blow at a high fan speed only. My mechanic was unable to resolve the problem. We switched the A/C switch control boxes between my '89 Deville and the '92 Deville and it still did the same thing. The '89 Deville fan speeds work perfectly and also cools to 38 degrees coming out of the upper vent. Any thoughts on what it could be? Thanks. Roger from Fort Worth, TX
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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6,738 Posts
Swap the fan power module under the hood in the evaporator case from each car and report back. It provides the changes in fan speed.
 

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99 Seville STS, 08 STS4 N* 1SG F55
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Carnut is right on. Remove the rear firewall cover in the engine compartment ( 2 x 10mm nuts) and the fan speed controller is just to the left of center on the firewall. Comes out straight up and is held in by 2 x 7mm hex screws. Has two wiring connectors on top.
 

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1989 Cadillac Sedan DeVille, 1992 Cadillac Sedan DeVille
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28 Posts
Discussion Starter #4
I will try your suggestion on exchanging the fan speed controller and let you know the results. Thanks.
 

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White Diamond '03 DHS (with DTS floor shift)
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I agree with Carnut & Chubby. Would have suggested that earlier, but I thought that was what you already changed.
 

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1989 Cadillac Sedan DeVille, 1992 Cadillac Sedan DeVille
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Discussion Starter #6
To those who replied to my message, I thank you. I checked with my dad (85 y.o. retired mechanic with Chrysler Plymouth who worked a lot on A/C's) who check with my mechanic. I found out that the mechanic had already tried swapping out the fan power module between the 89 Deville and the 92 Deville, but it still did not change anything. The module from the 89 Deville was installed in the 92 Deville and still just get the "low fan" speed, and the other four speeds just blow at the highest speed. When it is on any of the "auto fan speeds", it just stays blowing at the highest speed. I took both Devilles to his shop and this is when he swapped out the fan power module. I thought he had only changed out the control box on the dashboard. In fact, he forgot to switch the control boxes back to the orginal cars since the 89 does not have rear window defrost and the 92 does. If anyone else has any suggestions, please let me know. Thanks.
 

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1926 Model T street rod, 2000 Jaguar XJ8, 1999 Corvette.
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The fan speeds will lower from high once the programmer sees the interior temperature approching what you have set on the control head. So, my thought is the in car temp sensor is not sending the message to the programmer. Now thats with the assumption you have it displayed above 65 degrees. 60 and 90 are manual settings and will not regulate fan speeds, it will stay at max fan. With the glove box liner removed, you should see the aspirator hose going from the programmer to the little grille that takes in the interior air sample. If thats disconnected at either end, no signal will reach the programmer. If the in car temp sensor is electrically disconnected then that would also cause no speed regulation. This hose is black with a ribbed surface about 5/8 inch in diameter. Also, if that hose is kinked anywhere, it will delay or not allow regulation.
 

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White Diamond '03 DHS (with DTS floor shift)
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Make sure the aspirator fan is working also. Have you pulled the DTC's?
 

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1989 Cadillac Sedan DeVille, 1992 Cadillac Sedan DeVille
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28 Posts
Discussion Starter #9
Thank you Ranger and Carnut. I will check on these items you mentioned and get back with you on the results. It may take me several days but I will let you know.
 

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1989 Cadillac Sedan DeVille, 1992 Cadillac Sedan DeVille
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Discussion Starter #10
Carnut, I set the temp at 65 degrees today and the auto fans speeds worked properly now. :) I use to think it worked that way at 60 degrees, but maybe I am mistaken. Just like you said, when I changed it to 60 degrees, it blew high on the 4 highest settings. I just had the A/C charged last month as it had been over 3 years and I had never had it done and it was not cooling as well as it should be. Maybe small leak somewhere? Ifhave owned the car for 3 and half years and it now has 80K miles on it. It would only get down to 55 degrees out of the vent. It had slowly gotten worse over the three years. Now it gets down to 38 degrees. Will be 100 degrees today in Fort Worth. It uses R12.

On the 89 Deville, I can set it at 60 degrees and the fan speeds continue to work at all different levels. It does not just automatically blow high at 60 degrees on the four highest settings as it does on the 92 Deville. Maybe there is some difference between the 89 Deville and 92 Deville? The A/C also gets down to 38 degrees coming out of the air vent on this car. It was converted to R134 with new A/C installed.

Thank you Carnut and Ranger. I will continue to monitor the air speed on the 92 Deville. :thumbsup: If anything changes, I will let you know.
 
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