1985 vs 1986 IL4 V5 vs DA6 Air Conditioning Systems (Page 1/2)
Romsk JUN 04, 09:19 PM
I was recently informed about the V5 A/C system that was used on 1986, 87, and 88 Fiero 2.5L IL4 TBI models. I don't know much about the IL4 models so I read up on the V5 system.

I am told that the the V5 system was introduced in 1986 and that you must use a 1986 ECM with that system (for that model year). But 1985 and 1986 used the exact same ECM (1226864). I studied the 1985 DA6 system diagrams, the 1986 V5 system diagrams, and read the 1986 Service Manual section on the V5 system. The V5 has a clever variable compressor feature that makes it more efficient without cycling.

I made a brief video of my findings:
Fiero 1985 vs. 1986 Air Conditioning System Differences

My conclusion is that the 1226864 ECM (used for 1985 and 1986 IL4 ECMs) will work with either system. Each have different compressors, control/pressure/cycle switches, and relays, but they are all external to the ECM, so it appears that in the case of the 1985 and 1986 model years, either ECM will work with either the DA6 or V5 system. It makes sense that people are told to use a 1986 1226864 ECM with the V5 because that is the year the V5 system was introduced, but since the 1985 ECM is the same model, it should work just as well with the V5 system. I don't think the PROMS have any specific air conditioning parameters that make any difference between the two systems because each control their compressor cycling/variations externally from the ECM. The ECM is basically enabling/disabling the system connected to it.

Can anyone verify this?

------------------
Paul Romsky

cartercarbaficionado JUN 04, 10:13 PM

quote
Originally posted by Romsk:

I was recently informed about the V5 A/C system that was used on 1986, 87, and 88 Fiero 2.5L IL4 TBI models. I don't know much about the IL4 models so I read up on the V5 system.

I am told that the the V5 system was introduced in 1986 and that you must use a 1986 ECM with that system (for that model year). But 1985 and 1986 used the exact same ECM (1226864). I studied the 1985 DA6 system diagrams, the 1986 V5 system diagrams, and read the 1986 Service Manual section on the V5 system. The V5 has a clever variable compressor feature that makes it more efficient without cycling.

I made a brief video of my findings:
Fiero 1985 vs. 1986 Air Conditioning System Differences

My conclusion is that the 1226864 ECM (used for 1985 and 1986 IL4 ECMs) will work with either system. Each have different compressors, control/pressure/cycle switches, and relays, but they are all external to the ECM, so it appears that in the case of the 1985 and 1986 model years, either ECM will work with either the DA6 or V5 system. It makes sense that people are told to use a 1986 1226864 ECM with the V5 because that is the year the V5 system was introduced, but since the 1985 ECM is the same model, it should work just as well with the V5 system. I don't think the PROMS have any specific air conditioning parameters that make any difference between the two systems because each control their compressor cycling/variations externally from the ECM. The ECM is basically enabling/disabling the system connected to it.

Can anyone verify this?



if you tell me how to get data off of the prom i have a 84 auto, 85 manual with ac for prom chips and a 87 2.8 with ac so we can see if anything is the same

[This message has been edited by cartercarbaficionado (edited 06-04-2025).]

Romsk JUN 04, 10:51 PM
In the other thread, I told you about TunerPro for your S10. It can also read a PROM and show you all the data in it in human readable values.

But don't go through all that trouble for me... its rather involved. I was asking in case someone already had experience with my question.

Thanks,
Paul
fieroguru JUN 05, 07:14 AM
About the only thing the Fiero ECM does in regards to AC is turn it off at high RPMs and raise the idle speed.

All the cycling and compressor control are done by pressure switches, independent of ECM knowledge or control.

This means you can have working AC in a fiero with any or without any ECM (like carburetor swaps).
82-T/A [At Work] JUN 05, 08:11 AM
Hey Romsk, check out this thread I made a little over a year ago: https://www.fiero.nl/forum/Forum2/HTML/147877.html

RWDPLZ responded with a TON of information further down. He talks about the ECM, which still has me a little confused as to what the ECM does here, but this particular paragraph is important:


"Although shown in the same location in the diagram, the V5 low and high pressure switches don't perform the same function as the DA6/HR6 cycling switch: Rather they use the same input pin on the ECM. The V5 system also uses the fan control pin on the ECM to CUT the fan if pressures are too low (if pressure is too low, you'd actually want to warm up the condenser to increase pressure).

In order to use the V5 compressor in the DA6/HR6 car, you'd want to cut the signal wire to the cycling switch, and run new wires from that ECM pin to the switches on the compressor, wired in the same way. Note the locations of the C100 and C203 main connectors in the diagram in relation to the switches.

Again, I'd just put an HR6 compressor in the car and be done with it, far simpler and cheaper solution."


It looks like this information might be confirming what you've found in the ECM code. Sorry if I led you down a rabbit-hole... but I appreciate all the work you put into this. I think everyone should upgrade to the V5!

[This message has been edited by 82-T/A [At Work] (edited 06-05-2025).]

Romsk JUN 05, 08:21 AM
FieroGuru and 82-T/A,

Thanks.

My research yields just what FieroGuru said, the ECM has little to do with air conditioning other than to temporarily disable it at high RPMs, alter the Idle when the A/C is loading the engine, shut it down at high CTS temperatures (in case the Fan Switch fails), enable the Radiator Fan if the A/C is turned on (Il4s), temporarily disable it if the Power Steering is under high load, and monitor if the Compressor is on or off at the moment.

I will check out the link.

[This message has been edited by Romsk (edited 06-05-2025).]

Romsk JUN 05, 08:37 AM
82-T/A,

No worries... I love to learn... you have been very helpful in your collaborations.
RWDPLZ JUN 07, 10:14 AM
It's entirely possible the code to run a V5 compressor may be present in the 85 ECM's PROM chip - They may have planned to introduce the V5 compressor earlier than they did, and it was bumped to the following model year. It also may be present if it was used on other GM cars that had a V5 compressor, I doubt the computers and code were Fiero specific in an organization as large as General Motors at the time. If you actually found power steering code in it, that would also support the theory, as Fieros didn't have it and IIRC power steering prototypes weren't in development until 1986? and in cars until 1988.
Romsk JUN 07, 02:26 PM
Thanks,

I have never used TunerPro, so I have never seen what is in Fiero PROMs.

I agree, there is probably nothing specific for A/C from year to year in the ECM code or PROMs.
In the Repair Manual, it was mentioned that if the Power Steering is under high load, it will cut off the compressor. But even if virtually every Fiero didn't have Power Steeting, the signal is pulled inactive high internally in the ECM and thus defaults to inactive.

I assumed that on IL4 ECMs, the fans are turned on and the compressor is turned off if the CTS reads too hot (a backup for the Fan Switch on the Engine). The V6 ECMs don't control the Fan for some reason.

Adjusting Idle when the Compressor is on probably has just a flag in the PROM: 'Adjust Idle with A/C Compressor is On'. Since a Fiero with no A/C will never activate the A/C_On signal, I am sure all PROMs would have that flag enabled if A/C is installed or not. There is no feedback from the Compressor to the ECM, so it has no way of knowing how much load the Compressor is putting on the Engine, let alone what type of A/C System is used.

Thanks for confirming my suspicions.
Paul
richard in nc JUN 07, 11:05 PM

quote
Originally posted by Romsk:

Thanks,

I have never used TunerPro, so I have never seen what is in Fiero PROMs.

I agree, there is probably nothing specific for A/C from year to year in the ECM code or PROMs.
In the Repair Manual, it was mentioned that if the Power Steering is under high load, it will cut off the compressor. But even if virtually every Fiero didn't have Power Steeting, the signal is pulled inactive high internally in the ECM and thus defaults to inactive.

I assumed that on IL4 ECMs, the fans are turned on and the compressor is turned off if the CTS reads too hot (a backup for the Fan Switch on the Engine). The V6 ECMs don't control the Fan for some reason.

Adjusting Idle when the Compressor is on probably has just a flag in the PROM: 'Adjust Idle with A/C Compressor is On'. Since a Fiero with no A/C will never activate the A/C_On signal, I am sure all PROMs would have that flag enabled if A/C is installed or not. There is no feedback from the Compressor to the ECM, so it has no way of knowing how much load the Compressor is putting on the Engine, let alone what type of A/C System is used.

Thanks for confirming my suspicions.
Paul


im probably wrong but isn't the biggest fit issue if it bolts on and has the right pulley?