I am in the process of a F355 conversion and am doing the interior. To try and be a little more true to form I am attempting to convert all the heater controls to round knob style controls to mount in between the seats in a modified center console.

I have so far located the heater fan control as well as the temp control from a late model Grand Prix. They seem to interface well with the factory Fiero stuff. The only problem I am facing now is the selector switches above the slide control on the factory Fiero heater control. There are basically seven positions and I cannot seem to find the correct rotory switch to suit the application. The late model Toyota Camry uses electric servo type heater door controls and the dial seems correct, but not enough positions. This arrangement I would have to seperate the A/C into a seperate switch. Not a big deal but I am trying to stay with the Ferrari look and feel. The plastic surround area is no big deal as I will be fabricating this later. Ausfiero if you are watching let me know of any ideas on doing the backlit plastic surround :-)

If anybody has any suggestions let me know as I am kind of going brain dead researching this.

I have included some pics of the Grand Prix heater control to give everyone an idea of what I am trying to accomplish along with the F355 console. All suggestions are welcome.

Thanks to all!

[This message has been edited by 87fastback (edited 01-01-2002).]

Those heater controls might be able to me modified to work. First off, you've got an electrical switch for the fan, which is exactly what you need. For the mixer (hot/cold), you also have an electrical switch, but might I suggest this in order to allow it to work with the factory temp door: Remove all the electrical connectors, and make the knob just turn a lever that will pull or push in the factory temp door cable. you would obviously have to extend the cable a little to get it into the center consol location, but with the cable you've already got it might not be that hard.

But, for the actual HVAC controls, it will require a lot of modification. You might want to tear apart a stock HVAC control unit out of another Fiero and look how the connections are made when each particular button is pushed. Then, you could rip out all the vacuum logic stuff from that knob and install a multiposition pot switch (knob type switch, like mode selector on old home stereos and stuff).

It seems to me that the easiest thing would be to keep the stock pushbutton unit connected to all the servos (would be a pain to rewire all that), rip out the buttons, and have that multiposition pot switch emulate the buttons. In essence, all the circuitry in the HVAC control box would still be present, but instead of making certain connections with the pushbuttons, you'd be making them with that knob switch, which would be mounted in that panel and could have whatever knob you wanted on it.

I hope this helps!

It would be posible to convert from one type of switch to another for the door servos.

It's actually not very hard if you understand how the OE system works. just a real pain in the ____.

One thing you'll need to address.... the Fiero servo motors are current limited.

If you look at the Fiero controls, there are 2 small disk shaped components on the circuit board. Grey in color as I remember.... These are PTC Thermistors that limit current to the motors. They make the motors both easier to control and more reliable. It's a bit hard to explain but you really want to keep them in the circuit. (there's one for each motor.

what year GA are those out of? I'd be interested in them for other reasons....

If you are planning to use the actual controls shown....

The Controls shown may be a good bet. BUT....

Before you can even consider this, you need both the Fiero wiring and the GA wiring. You likely need several pages of the GA schematics to work it all out. The systems those controls run are commonly spread over several diagrams. The same would hold true of most other controls you would use.

I have a suspicion that those controls you show are incomplete. Systems that provide temperature control like your bottom photo nearly always have additional temperature sensors and often a brain box to monitor cabin temperature. It could be done "in the switch" but w/o the schematics for that Grand Am, I couldn't tell you.

the heater motor is the easy part. The mode motors are a bit harder. the most interesting part will be what looks like a combination of servo and control for the blend (temp) door.

If that thing works the way it looks....
The blend control is nothing but a variable resistor. (like the dash dimmer) It's used with a temperature sensor and likely some other logic to work a motor inside the control head. the motor in turn works the blend door.

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11-Sept-01, The day the world as we knew it ended.

Crap.... that's a vac setup??? I couldn't hardly tell....

I didn't catch the thing rotated in the top/bottom views....

In that case,,, no. the mode controls won't work. Very likely Neither will the fan motor switch. The wire gauge used there indicates it may not handle the current. You could end up with relays for each speed compared to Fiero having a relay only on High.

what I said about the blend control is likely still correct. I still want to know what they are out of.

The controls came out of a 1998 Grand Prix or Grand Am, I really can't remember but it dosen't matter anyways - they are both the same. I actually have 2 units here, the one pictured and another out of a different car that has a black defrost switch. If you need it let me know as I can ship it over to you.

As far as the blower motor and blend switch, that is covered. The blower motor switch will work with the Fiero motor. I have to rewire it of course but it works nonetheless.

The blend switch is just a rotory knob with a gear arrangement inside that actuates the cable shown. I have to lengthen the cable, but that is also no big deal.

Yes you are right about the mode switch. It is vacuum in the picture, as are all other GM vehicles. I looked a LONG time at the wrecking yard and then finally figured out nobody else uses electric servos for the heater box doors. Chrysler products use electric servos, but they use a very complex computerized head unit for control - not easy to do.

Funny thing though, I went to work the other day and hopped in a new Camry (I work for Toyota) and low and behold the controls looked like what I needed. Then upon further looking I found that the ode switch is electric. But the bummer part is that these units are sold as 1 piece and VERY expensive.

FieroJoe mentioned using a rotary pot like from a home stereo application, that might just work. If not I think his idea about interfacing with the factory Fiero head unit might also be a solution - bulky, but it would work!

Thanks and keep any other ideas coming!

Oh and Ogre, let me know if you want this other control.

quote Originally posted by theogre: Crap.... that's a vac setup??? I couldn't hardly tell....

I spotted that first thing. I've worked on a few newer style HVAC controls that have vac logic, its pretty interesting stuff. I also figured those were vacuum lines becuase they were so much bigger than all the rest, couldn't see why that large a gauge of wire would be in a switch that small.

As for the thermistors, I don't know how they work, but, let me try to think out loud here:

When a button is pushed to start a door servor in motion, all the current travels though a transistor, which has these thermistors on its base. The current also travels through the thermistor. When the door shuts, it draws more current, making the thermistor heat up and increase resistance, which eventually cuts off collector to emitter flow on the transistor?

Or have I just spouted a bunch of crap? Without looking at the diagram and only having minimal experience in circuit board electronics that's the only rationalization I can come up with.

I'd just swap out all of the old stuff and build your own controls from your desired rotary switches. Adapting something actually sounds like MORE work!

I'm planning a thermostatically controled system for the Northstar car eventually, similar to what you see in better new cars these days (Orgionally done by Mercedes in the late 80s I belive.) Still can't decide if I should bother to try to adapt/convert an existing automotive AC brain/sensors, or build my own from the ground up. In that case, it's kind of a tossup (as the stuff to actually switch between heat/cold/defrost/vent/high/low/etc would be extra in the you-fab-it route.)

Best!
Ben.

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Ben Cannon
88 Formula, T-top, Metalic Red. "Every Man Dies, not every man really Lives"
88 Formula, Northstar, Silver, In-Progreess. -Mel Gibson, "Braveheart"

Why don't you try a rotary switch?? They come in all sorts of positions (i.e., 5, 6, 7, etc.), and can handle REASONABLE currents.

Looks like an interesting prioject... I can offer my services if you'd like (see my article about O/H console, and Backlit power window switches in Ogre's Caves)

LMK

Bill

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Bill Osmer

quote Originally posted by 87fastback: I am in the process of a F355 conversion and am doing the interior. To try and be a little more true to form I am attempting to convert all the heater controls to round knob style controls to mount in between the seats in a modified center console.

I've done quite a bit of work on the Fiero climate controls... Here's some info that should help with your project.

The connector to the climate control PC board has thirteen connections:

A - Illumination lamp supply
B - Fan power (hot if OFF not pressed)
C - Illumination lamp ground
D - Hot to get DEFROST outlet
E - Hot to get FRESH inlet
F - Hot to get BILEV outlet
G - A/C on signal to ECM
H - GND for engine cooling fan relay
J - Hot to get VENT outlet
K - Engine cooling fan relay enable
L - Hot for RECIRC inlet
M - Hot for FLOOR outlet
N - 12V power to the control unit (hot in run)

Note that there is no "I".

Also note that "A" is on the passenger side of the car with the unit installed in the dash.

The PTC's that Ogre mentioned are there to protect the motor and the control switches in the event that the motor gets jammed and tries to draw lots of current as a result of being stalled.

The system will function just fine without them but do realize that you are increasing risk of burning something out in the off chance that you stall a motor.

There are no transistors involved. There are no active components in the Fiero control head. The PTC's resistance is very non-linear with temperature and when they get too hot, the resistance shoots way up and cuts off the current. Shut the system off (read "turn off the key") and let the PTC cool off and it will "reset".

My recommendation would be to throw the vacuum controls as far as you can and either keep looking for an electrical donor or use a rotary switch from Radio Shack.

Hope the above is some help!!

-Bruce at FTF Engineering

Ok, I'll see if I can explain this more while I'm still awake.

There are no transistors in the Fiero system. Just those 2 PTC thermistors.

This will be easier if you have the Fiero heater control diagrams in front of you while we do this... (That will include the mode door diagram and AC diagrams at the least.) The mode door diagram is the last one in Haynes...

If you look at the diagrams carfully, there are three layers of control.

One for each door servo and one for the AC enable.

Both motors while wired somewhat diferantly, function the same. The only differance is that the recirc door has 2 stops and the mode door has 4.

The job of the thermistor is to make the motors easier to control. The thermistors are labeled RT1 and RT2 in the diagram. (Keep in mind PTC means Positive Temperature Coefficient. That means the resistance goes up with temperature. This is the oposite of engine sensors which are NTC, Negative Temp Coefficient, meaning their resistance drops with temp.)

When you push a button, the thermistor is cold and low resistance. That lets the motor have more juice to kick over. (Handy in cold weather when it's lube gets a bit stiff.)

The current the motor draws warms the thermistor. This increases it's resistance and reduces power to the motor.

This has the effect that when the motor reaches the stop point on the servo wheel, it stops dead in much less time. That prevents the motor from overshooting the stop point which is rather small.

To convert to a knob...

You need a 3 section selector with 7 positions. (Assuming you want all the original Fiero functions.)

You'll use a section for each door servo and the third to enable the AC system.

In all honesty.... the mode door diagram in the haynes book has nearly everything you need to wire this up. you shouldn't need anything off a Fiero control set but those thermistors. there's no need I can see for trying to trace out the OE fireo control head.

There are selector sets of all types. If you can't find a prefab one there are sources to get the parts for to make all sorts of configurations. (No, I can't think of who right now...)

So are these thermisors something I could get from Digi-key or something like that? I kind of see where this is going and I looked at the wiring diagram in the haynes and on Alldata - which by the way are exactly the same. They looked pretty straight forward, especially the mode door diagram. It actually helped me the most. Thanks for the tip on the type of switch to use. I thought I would end up with a 3 pole 7 position, but just wanted to hear it from someone more educated than me before I started spouting off my big mouth.

Thanks Bruce for the pinout, that helps ALOT! I am trying to locate the switch now, so as soon as I find that I will start soldering it up.

Thanks for all the help and I will post my results after the weekend.

Brent

Just a thought but have you though of replacing the whole heating system with one out of a car that has the approriate controls. The Fiero heater is rather large anyway so fitting another in shouldn't be a great problem. That is what I am thinking about doing as for some reason most Fieros in Australia do not have working heaters after RHD conversion. Don't ask me why, I don 't know.

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