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V8 swap/AC questions by fierov8
Started on: 01-17-2004 08:51 PM
Replies: 7
Last post by: fierov8 on 01-18-2004 07:26 PM
fierov8
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Report this Post01-17-2004 08:51 PM Click Here to See the Profile for fierov8Click Here to visit fierov8's HomePageClick Here to Email fierov8Send a Private Message to fierov8Direct Link to This Post
This one is for all the experienced swap folks -- I need help with the air conditioning!!!

Here is what I have -- V8 with ECM from 1991 Corvette. I have both service manuals (Fiero and Vette) and it appears that the circuits for running the compressor are different on both vehicles. I'm sure someone out there has done this -- does anyone have a circuit diagram or some helpful direction on how to merge a Fiero compressor, a Vette ECM, and the Fiero dash controls?

Many thanks in advance!!

-jeff d
Fort Worth, TX
198? Fiero GT/V8
1973 TVR 2500M

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fierov8
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Report this Post01-18-2004 12:42 AM Click Here to See the Profile for fierov8Click Here to visit fierov8's HomePageClick Here to Email fierov8Send a Private Message to fierov8Direct Link to This Post
TTT -- anyone? Help!!

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Darth Fiero
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Report this Post01-18-2004 09:08 AM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
Yes, if I remember correctly the 91 Vette ECM controls the A/C compressor clutch directly. The Vette ECM looks for an input signal from the heater controls and A/C pressure switch.

Ok, just looked at the diagrams for both cars. Here is the deal. The 91 Vette ECM looks for what appears to be a ground signal on PIN B15 from the A/C controls to determine when the A/C is being requested. According to my diagrams, it looks like when the wire that goes to PIN B15 is grounded, the ECM thinks the A/C is being requested. Now this is different from the Fiero in that the A/C controls for the Fiero supply IGN B+ voltage to the A/C "request" wire instead of grounding it so you will have to hook up a relay in the following way to interface the stock Fiero A/C controls with the Vette ECM...

Using a standard 5-pin relay, if the stock Fiero A/C harness and relay are not present:

Term 85 hook to GROUND
Term 86 hook to LIGHT GREEN wire coming from A/C controls
Term 87 hook to GROUND
Term 30 hook to Vette ECM term B15

If you still have the portion of the stock Fiero engine harness that has the A/C relay, hook the additional relay up like this:

Term 85 hook to GROUND
Term 86 hook to LIGHT BLUE wire that goes to the stock Fiero A/C relay Term A
Term 87 hook to GROUND
Term 30 hook to Vette ECM term B15

This should take care of the A/C request part of the Vette ECM but there is more...

If you are using the stock Fiero A/C relay and harness, you will need to hook term A13 of the Vette ECM to the DK BLUE wire going to PIN C on the stock A/C relay, which is located next to the Fuel Pump relay in the engine compartment. If you have removed the stock A/C relay and harness, hook up a standard 5-pin relay in the following way:

Term 85 hook to LIGHT BLUE wire coming from stock A/C cycling Switch
Term 86 hook to Vette ECM pin A13
Term 87 hook to Fused IGN B+
Term 30 hook to A/C Compressor Clutch +

The 91 Vette ECM also wants to monitor the A/C clutch status. Connect the Vette ECM Term C17 to the + side of the A/C compressor clutch.

This should take care if it. Hope this does not confuse you more... Let me know if you have any problems.

------------------
power corrupts. absolute power corrupts absolutely.

Custom GM Chip Burning | Fiero Engine Conversions | Turbocharging | dtcc.cz28.com

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fierov8
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Report this Post01-18-2004 12:05 PM Click Here to See the Profile for fierov8Click Here to visit fierov8's HomePageClick Here to Email fierov8Send a Private Message to fierov8Direct Link to This Post
DarthFiero,

A "+" for you for the help!! No confusion here at this end -- I've rewired the entire car, so what you're saying makes sense to me. At least it makes sense here just looking at the computer -- things might change once I get my mitts on the car again :-)

One question on the Fiero -- where is the A/C cut out switch located?? Is this one of the connections on the back of the compressor?? I know the pressure cycling switch is in the front compartment near the accumulator, but the manual is less than clear where the A/C cut out switch is :-(

Thanks again for the help -- gonna try to go out in the garage and start to see if this all makes sense........

-jeff d

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fierov8
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Report this Post01-18-2004 12:41 PM Click Here to See the Profile for fierov8Click Here to visit fierov8's HomePageClick Here to Email fierov8Send a Private Message to fierov8Direct Link to This Post
Darth -- one thing........

In your notes you reference term 85, 86, 87, and 30 -- one little bit of confusion here. Can you "translate" what pins these are for me? Let's say I was referencing the A/C Clutch Relay diagram in the Fiero Electrical Manual, pg. 8A-64-0 -- how do your pinouts map to pins 1, 2, 4, and 5 on that diagram?

thanks!

-jeff "still needs more coffee" d

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fierov8
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Report this Post01-18-2004 12:49 PM Click Here to See the Profile for fierov8Click Here to visit fierov8's HomePageClick Here to Email fierov8Send a Private Message to fierov8Direct Link to This Post
never mind that last question -- as always Google is my friend:

http://www.mechanical-relay.com/dy8_42.html

relay schematic is at the bottom....................D'OH!

-jeff d


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Darth Fiero
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Report this Post01-18-2004 05:09 PM Click Here to See the Profile for Darth FieroClick Here to visit Darth Fiero's HomePageClick Here to Email Darth FieroSend a Private Message to Darth FieroDirect Link to This Post
 
quote
Originally posted by fierov8:

DarthFiero,

A "+" for you for the help!! No confusion here at this end -- I've rewired the entire car, so what you're saying makes sense to me. At least it makes sense here just looking at the computer -- things might change once I get my mitts on the car again :-)

One question on the Fiero -- where is the A/C cut out switch located?? Is this one of the connections on the back of the compressor?? I know the pressure cycling switch is in the front compartment near the accumulator, but the manual is less than clear where the A/C cut out switch is :-(

Thanks again for the help -- gonna try to go out in the garage and start to see if this all makes sense........

-jeff d

Some Fieros had the pressure cycling switch on the accumulator up front. Those that don't have it on the A/C compressor. The HI-Pressure cutout switch is on the A/C compressor, usually red colored connector.

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fierov8
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Report this Post01-18-2004 07:26 PM Click Here to See the Profile for fierov8Click Here to visit fierov8's HomePageClick Here to Email fierov8Send a Private Message to fierov8Direct Link to This Post
Yeah -- that sounds about right -- there are two connections on the back of the compressor, each with a single connector. One has a clear housing around the terminal, the other has a red housing. If the red one is the high pressure cutout connector, the other one is what then???

Thanks!!!!

-jeff "automotive a/c was never a specialty of mine...." d

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