It was getting nearer to summer and all I could remember was how hot that last summer trip to New Jersey was last year.  The trip back was OK because the weather had taken a turn for the cooler.  I decided to do some experimenting to see just what could be wrong.  

The air was blowing sufficiently cold air from the vents (about 40 degrees) but the volume at high speed was about what I had remembered it was at low speed although the blower motor was screaming along like a banshee.  Something was impeding the flow of air in the system.

The first thing I suspected was the airflow control system.  This car is a 92 Bonneville SSE, with just about all the bells and whistle one could imagine.  The heating and cooling system was no slouch.  It was electronically controlled and had a thermostatically control set of baffles which directed the air around the evaporator to mix with warm air from the heater core to control the air out temperature.  That was my first target.

I went to the library and got the shop manual for the car.  Every job is so much easier with the manual - I'd suggest that anyone starting a job much more complex than an oil and filter change get the shop manual before starting the job.

Once I had read all about the control system and the sophisticated vacuum controller I was pretty much convinced that my first theory was wrong.  I had thought that perhaps the controller had closed two or more baffles at the same time thus preventing air flow from coming out at its maximum rate.  Wrong - there was no way that could happen.

Next, I suspected that there might be an obstruction in the air path somewhere.  This car is stored each winter to keep it out of the salt they spread up here in the north country and I suspected that mice or chipmunks might have somehow gotten in the air ducts and made a nest in there, perhaps inside the squirrel cage on the blower motor.  So I pulled the motor and squirrel cage and it was as clean as a whistle.  While I was in there I looked inside the heater plenum to see if there was something in there - nothing!

Next, I decided to go visit my friend, Steve (a service manager) at the local Pontiac place to ask if he had any ideas.  He suggested that I take a look at the evaporator to see if it is contaminated or clogged.  But if you ever tried to get to an evaporator core you know it is a five hour job.  Buttttt, my friend had a better idea.  He suggested that I could access the evaporator core, at least to see it, via a rather large hole in the plenum where the heater blower motor controller is located.  It is underneath the relay bank on the firewall.  (see photos)

I removed the relay bank on the firewall by removing the two fasteners on either side of the chassis and pulled the relay assembly to the side.  There was the blower motor controller, visible only as an irregularly shaped plate secured with four screws to the top of the heater plenum.  I removed the screws and disconnected the electrical connector from the top.  The unit consists of a long aluminum finned heat sink which contains a resistor bank which is used to control the speed of the blower motor.  I lifted it out of its recess in the plenum and set it aside.

Now, using a droplight, I peered inside the hole.  I could see a rectangle about 8 X 8 inches which looked like a piece of black felt.  I thought it was some sort of heat shield or insulation.  Upon further inspection I realized that it was the surface of the evaporator core, totally covered with dark fuzz - road dirt, tree pollen and just about everything that was sucked into the heater system from outside!!

I got a spray bottle and filled it with a concoction of hot water, laundry detergent, degreasing solvent and dishwashing detergent.  I sprayed this solution onto the black felt-like surface and watched it melt away and downwards towards the drain hole in the bottom of the plenum.  The stuff that came out onto the driveway was disgusting but also very satisfying to see that I had indeed found the reason why no air was circulating through the air conditioning system.  I follow the detergent treatment with a garden hose set on a spray pattern and continued flushing the crud out of the system until the evaporator core looked like a shiny aluminum evaporator core, not like a piece of carpet! Ten minutes later I shut the hood on a very satisfying job.

The air now flowed harder than I had remembered it had for years!! I was happy to be able to use the Pontiac for the next summer road trip to NJ and ecstatic when my wife asked me to turn it down a bit since it was blowing too much cold air on her!

Back to the index page (top level)

Copyright © 1996, 1997, 1998, 1999, 2000, 2001, 2002 by Bob Hewitt - All rights reserved