On Monday I was cruising Saabnet when I saw reference to using the dash-mounted A/C switch (on cars with inoperative A/C) to control the second radiator fan. The first fan is thermostatically controlled based on coolant temp, but that second fan runs only when the A/C is on and functional. Each fan covers approximately ½ of the radiator, so if the A/C isn’t on, you’re only ever passing air through half of the radiator if you’re at a stop. That leads to potential for overheating in hot weather, a known problem in the classic 900.
From the factory, the A/C radiator fan is controlled with the A/C compressor clutch by pressing the dashboard-mounted A/C button. This is interlocked with a temperature sensor in the heat exchanger for incoming air to be cooled (turns off the A/C when a low-limit is reached), and with a refrigerant pressure switch (prevents A/C from being turned on when insufficient refrigerant pressure exists in the system).
By putting a jumper across the two terminals of the refrigerant pressure switch, it takes that device out of the circuit, allowing the A/C radiator fan to be controlled by the dashboard-mounted A/C switch. As long as the temperature is above freezing at the air inlet, that fan will run when the A/C switch is on. I added this jumper, it was an easy 5-minute mod that will help the car run cooler on hot days. It’s amazing how much fluctuation of the temp gauge I would see on hot days, especially when in slow or stop-and-go traffic. So there is the added cooling.
The lost cooling I referred to is, unfortunately, the loss of sunroof function. The 900’s electric sunroof is driven by an electric motor located under the trunk floor at the very back of the car. The motor drives a small gearset which in turn drives a ball-screw type cable to open or close the roof. The cables run from the trunk, up the C-pillars, and to the sunroof assembly.
When I bought the car, the sunroof was duct-taped closed. I think that was done to prevent water from leaking into the car through clogged sunroof drains. I took the tape off and cleared the front drains, though the rear drains remain clogged (I tend to park with the nose of the car pointing downhill for that reason in rainy weather). The electric sunroof worked, though it clunked/jerked when opening, sounding like a gear was missing a tooth or two.
In the past few weeks, the roof has slowed down significantly, and the clunking has increased, as though more teeth were missing from this gear. By posting an inquiry on Saabnet, I was able to discover that all of the gears are a part of the motor assembly; the cables are the only things attached to the sliding roof panel.
On Monday I drove the 900 to The Home Depot to get some 10’ pipes for Ani to build a puppet stage. The roof was so slow to open that I ended up just pushing backward on it once it began to open. And I was able to push it freely with my hand. Uh-oh.
When I got home, I was parked with the car pointing uphill. I tried the switch to close the roof, but it didn’t really work, gravity of the car pointing up hill kept the roof in place. I finally pushed from the bottom of the roof and got it closed. It was evident that the gear had no teeth left.
This morning I did a quick inspection of the motor assembly. I un-mounted it from its place in the trunk, and took off the cable retainer (which frustratingly uses 3/8 inch nuts, rather than something metric… I had to go find my “imperial” sockets. It’s prolly because the motor itself is made by Lucas Electronics Why Saab would use these I can’t comprehend, but I digress. It’s another of the ‘80s add-on features that were put on this fine car designed in the ‘70s and produced in 1992). What I found once I finally got in there was exactly what I had feared: the gear’s teeth were all worn off.

I checked The Saab Site’s 900 FAQs and parts list, and found that that gearset isn’t available by itself; the entire motor assembly ($460) must be purchased. Curiously, the cables are also available for $160 apiece, two are used in the car. I’m afraid that the teeth on the gear failed because the cables are binding, either because they simply ran out of lubrication or because the roof is not riding properly on its tracks. In either case, the force to move the cables is greater than the gear was designed for, so it’s likely that even if I could replace the gear, I would end up wearing it out too.
So the long and the short of it is that the sunroof is inoperative. Which is sad, because I really like driving with it open. Time to look into retro-fitting a manual open/close assembly, which was used before the electric drive was implemented.