New'n72

1972 Cutlass “S” with factory air.. Air conditioning unit was upgraded 4 years ago. At the time of the upgrade I had only 3 of the 4 fan speeds. The third highest speed did not work.

After the air conditioning unit was upgraded ALL fan speeds worked. I had all functionality in the Normal and MAX settings.

Sometime later (approx a year) the third highest fan speed failed once again. I still had all other functionality in the air conditioning and fans.

About a month ago, the wife and I were out in the Cutlass one evening and decided to use the Air. It was during that real hot 90+ temp and 90+ humidity period we went through in the mid-west a few weeks ago. All I could get out of the system was hot air. No cold air. All settings on the dash panel seemed to work (except for the number three fan speed) but no cold air!

I took it into the shop and they recharged the unit and put some dye in the system. Last week I drove it for the first time since then. I drove it to work one day (10 mile one way) and on the way home I set the lever on MAX and exercised the Air system. Everything seemed to be working fine until I almost got home. At about mile 9 of my 10 mile return trip everything just quit! High fan stopped and MAX setting produced no cold air. I ran the lever through the fan speeds and I had only the lowest two. I also moved the lever from MAX to Normal and had cold air in the Normal setting only.

So….I have Air Condition in Normal only and only the lowest two fan speeds.

I will apologize up front for not being much of an auto mechanic. My only claim to fame here is that I bought this Cutlass 40 years ago and kept it. I DO think that I could fix this; however, if I could only locate all the pieces to the puzzle.

I have tried to figure out why that number 3 fan speed didn’t work, in the past and looked for the resistor block without success. Besides the resistor block for the fan speeds, I read another post here regarding air-conditioning that said the MAX setting apparently bypasses the resistor block. I assume that means a relay someplace????

I have the GM/Fischer manuals for this model year with a wiring diagram.

Can anyone suggest a method/approach to troubleshooting this? Help locating that resistor block and whatever is involved with the MAX setting, would be a start.

Thanks in advance for any assistance offered.

Regards,

Robert

Lady72nRob71

Get you fan working first - that should be easy.

Resistor is buried below the POA valve and section hose. It is on the side of the evap case with 4 wires going into it. Mine is red - see below.

The wiring could be bad (mine worked but was melted down) or the resistor bad. Remove it (2 9/32" screws and you can check it.

Here is the stock 72 AC wiring:
https://classicoldsmobile.com/forums...tml#post308282

The MAX AC position brings in mostly inside air rather than outside.
It is possible the switch on the selector lever may not be engaging the compressor.

The HI fan speed uses the relay by the brake booster and a 30A inline fuse from the horn relay. Check that fuse. The holder might be fused together from the years. (No pun intended there...)

Hope this gets you started. At least the freon part is okay.

New'n72

Rob,

Thanks....it amazing what a little bit of knowledge will do. I looked at those pictures in the service manual a dozen times and could not relate the resistor in the schematic to the resistor in the drawing. Guess I was expecting different wording/(Resistor block, fan control resistor or some such thing.)

I'll go through the checks in the service manual for the blower too. I haven't do that yet.

Thanks for the pic!

Robert

New'n72

OK...update: The Third fan speed is dead due to a broken connection at the resistor. The plastic plug is melted on the bottom and the wire and terminal are rusted and not touching. Since the plastic is melted there is nothing to hold the wire or connection together. I clipped the wire to the terminal and I had fan at position three if the switch.

The high fan failure was due to the connections at the high fan relay. I wiggled the connectors around and I had high fan.

The high fan is fixable; clean the terminals and re-seat the connectors.

That plastic plug on the resistor may be a problem for me? I see that I can get the resistor and/or the complete harness including the plug for the resistor but I don't see that I can get the plug by itself.

Any suggestions?

Regards,

Robert

Lady72nRob71

The resistor connector is available thru Rockauto - about 10 bucks to your door. It is black though...
It has 6" or so leads but you can remove them and replace them with your own or solder your wires onto their new contacts.

Attend Rob's Skule of Terminal Repair to see if yours may be salvagable:
https://classicoldsmobile.com/forums...tml#post312739