the flyin' scotsman

Was wondering if I can 'update' my '88 HVAC to the newer Hvac head with the Recirc button.............is the wiring the same or totally *** bkwd?

TIA

SeanR

This is something I've been trying to figure out too. I just need a GTS head unit to play with.

the flyin' scotsman

If i have it correct the recirc flap on the '88 MY is controlled by the auto system and sends or restricts the vacuum i/p thru the solenoid via the string from the outside and inside sensors.

I assume ( yes that dangerous) that the 'newer' systems overide some of the auto i/p when the recirc button is depressed..............Alan?

Alan

Malcolm,

I wouldn't bother - the functionality is not much different than you already have mainly the naming is different. Recirc mode is more or less the same as 'Off' in the earlier cars. There is no real 'off' for the system and no real 'off' for the blower either*. In 'off' you get recirc with whatever blower speed you select and and can also have AC on or off. There is some override control on recirc but this equivalent between '88 and the GTS systems.

* Except '94-'95 blowers

I think they are actually pin compatible but I haven't checked everything - I just don't consider it to be that worthwhile of a swap.

One day I will rework my HVAC head unit. When I do I will change the recirc to be basically just a switch - my choice. I will also change all airflow flaps & hot water valve to be purely electrically operated (what were they thinking...). I'd combine the rear air flow & front temp setting to a single temp **** (rotary) and also combine the rear air fan to just have an on/off switch and have its fan speed be controlled by the same rotary **** as the front (when on). The fan speed control for front & rear will be fully variable (a new design). Defogger (DEF) mode will be just an on/off override button too. AC stays an on/off as now. Flap control will also be rotary but 4 positions only Up+Vent, Down+Vent, Up+Down+Vent & Vent Only. I'd consider this a close to optimal control arangement given the basic system configuration.

Alan

the flyin' scotsman

thx Alan..............I posted sometime ago of replacing of the vac operated flaps with electric servos akin to what I use in RC choppers. While the idea remains the manufacturing is delayed by other projects. Although we think same as to controls I dont have rear air to worry about.

My truck system is fine; perhaps I'll raid the scrap yard when next in the big city.

heinrich

Alan in the 87... pulling the switch all the way to the left sets the recirc flap closed and turns the fan off completely. No air enters the cabin and no air is recirculated inside it. Seems less useful *than to have the flap close off outside air and still be able to recirculate air inside the cabin with the fan ***which the 87 does not do.

Alan

H - Oh OK I need to look at that again. I've mostly investgated the GTS of course.

In any case even on a GTS Recirc is a fixed single configuration with predefined flap controls - footwell & defogger vents are open - it does engage AC automatically which is a difference... Its not terribly useful as a cooling mode since you cannot ever get max flow to the face vents. I that's why I'd like seperate control of the recirculation - much more useful in hot climates.

Let me check for the difference in system on/off control - an a GTS the system (blower relay) is energized just by connecting the head unit - no head unit controls make any difference to this.

Alan

heinrich

Alan I agree, a separate recirc button is all we need. Then we can run the system heat or ac or any fan speed with either inside or outside air. How can I help you make this a reality Alan?

heinrich

Incidentally do the new cars have a recirc button? I think not .. it is a slider position, in other words you cannot use the recirc while you have the system on anything else.

87 -> OFF position -> all controls unresponsive (fan, interior flaps etc), outside air closed off
later cars -> RECIRC position -> ac on, outside air off, fan active, interior air diverted to feet etc

the flyin' scotsman

H............you are correct it is the slider but I do believe the recirc is also operational in other settings as is your MY and mine.

If the recirc was electrically controlled per my servo idea with a button we would be good to go. Winter project #372

Mike B

Damn Malcolm...we have months before winter...say it with me. Summer hasn't even got here...I know 'cause my car was going to be on the road for summer!

Earl Gillstrom

I went the other way and it works fine. My '91 head was destroyed in the fire and I put in an '88 HVAC head and it works like an '88. The only difference seems to be no recirculate.