AC blower acting funny
Thread Starter
Instructor
Joined: Sep 2002
Posts: 137
Likes: 0
From: Toa Baja Puerto Rico
AC blower acting funny
My 87 Coupe has electronic AC controls. When I switch on the AC the digital display shows the blower speed at 10 (the highest). After a few minutes, the blower speed drops to about one-half, although the display still shows 10. A few minutes later it goes full speed again. It keeps doing this all the time, even when the car is standing still. The AC evaporator is clean, the compressor is 2 years old and it has a full charge. I took it to two different shops and the guys there did not know if it is supposed to work like that or not. Anybody has had this problem? Is there an easy fix or is this the way it is supposed to work. The temperatures down here in Puerto Rico are in the 90's and with the humidity factor it feels in the 100's. Any help out there?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Re: AC blower acting funny (alfonso gomez)
The dash assembly controls blower speeds based on the temperature and mode selected and electrical inputs from the inside & outside temp sensors. When it's on auto "60", it's suppose to ignore the temp sensor inputs and keep the blower on max. This setting also produces a higher blower speed than the manual "10" regardless of temp setting. It should do the same when on Auto "90" for heat. At all other auto temp settings - "65" to "85", it's going to vary blower speed. When in manual mode, it should maintain blower speed at the manual setting. If yours isn't doing that, it's generally a bad dash assembly, but it could also be the temp sensors are out of range or a funky blower module. Difficult to troubleshoot, but one thing you could do is monitor the blower motor voltage signal by backprobing the brown wire at the blower module. It's mounted on the evaporator housing on the right side of the firewall. When it's on Auto "60" that wire should have a constant reading above 6 volts. If it drops below that, the dash assembly is probably bad. If it stays there, but blower speed drops, then the blower module is most likely at fault.
