Final Steps for A/C - Relay/PCM control? Electronics gurus?
06-29-2007, 08:12 PM
#1
TECH Regular
Thread Starter
Join Date: May 2005
Location: Bay Area, CA
Posts: 406
Likes: 0
Received 0 Likes
on
0 Posts
Final Steps for A/C - Relay/PCM control? Electronics gurus? Well, time to show my extreme limited knowledge in reading electronics diagrams. Anyway, about to finally get the A/C working in the swapped car. I am using the entire 4th gen HVAC assembly, the box, the HVAC controls, the compressor, condenser, lines, hoses, everything. My engine harness hasn't been modified at all. I have run the A/C request wire from the control assembly to Pin 17. What I need help with is understanding Pin 18 and Pin 43 and their relationship to the relay. How do I hook this up? What kind of a relay will I need? The harness I had made for the swap uses all the stock connectors so if wiring needs to be done there it can be.
I'd appreciate the help if someone could take a look at the attached wiring diagram and break it down a little for me.
I'd appreciate the help if someone could take a look at the attached wiring diagram and break it down a little for me.
06-29-2007, 08:39 PM
#2
TECH Fanatic
iTrader: (31)
Join Date: Apr 2007
Location: Dover DE
Posts: 1,207
Likes: 0
Received 0 Likes
on
0 Posts
The A/C request signal from the dash dosen't energize the clutch like in older cars. It sends a signal to the PCM which in turn supplies a ground at pin 43 to energize the relay. Power from the relay enters the PCM on pin 43 so the PCM can verrify the clutch has been energized.
Re'
Re'
06-29-2007, 08:40 PM
#3
Ok here goes... I used all the parts of a 99 a/c system in my 87. I also retained all of the engine wiring harness, along with the factory fuse boxes. So I didnt need to worry about the relay.
However...maybe i can help shed some light. Pin 43 is the actual pin that triggers the compressor. The A/C request signal, 12v on pin 17, sets things in motion as far as the PCM checking the pressure switch and all that. Then the PCM grounds the compressor relay via pin 43. When it does, 12v comes from the relay, down to the compressor clutch. It also goes to the PCM through pin 18. I believe that this is referred to as the a/c compressor status signal. It lets the PCM know that the a/c compressor is on and should be locked up. Not 100%, but it might change things slightly such as idle speed and what not.
So I think thats all that is...just letting the PCM know that the compressor is on. If you have all of the original wiring, it should be pretty easy. Just give the a/c request pin 12v from the hvac controls, hook up the relay just like it is in the diagram, and viola. Should work for ya.
Hope that helps...
Justin
However...maybe i can help shed some light. Pin 43 is the actual pin that triggers the compressor. The A/C request signal, 12v on pin 17, sets things in motion as far as the PCM checking the pressure switch and all that. Then the PCM grounds the compressor relay via pin 43. When it does, 12v comes from the relay, down to the compressor clutch. It also goes to the PCM through pin 18. I believe that this is referred to as the a/c compressor status signal. It lets the PCM know that the a/c compressor is on and should be locked up. Not 100%, but it might change things slightly such as idle speed and what not.
So I think thats all that is...just letting the PCM know that the compressor is on. If you have all of the original wiring, it should be pretty easy. Just give the a/c request pin 12v from the hvac controls, hook up the relay just like it is in the diagram, and viola. Should work for ya.
Hope that helps...
Justin
06-29-2007, 08:41 PM
#4
Originally Posted by RE AND CHERYL
The A/C request signal from the dash dosen't energize the clutch like in older cars. It sends a signal to the PCM which in turn supplies a ground at pin 43 to energize the relay. Power from the relay enters the PCM on pin 43 so the PCM can verrify the clutch has been energized.
Re'
Re'
J.
06-30-2007, 10:09 PM
#5
TECH Apprentice
Join Date: Aug 2005
Location: Dover Arkansas
Posts: 347
Likes: 0
Received 0 Likes
on
0 Posts
Yea, if your using the UFB(underhood fuse box), the relay is on there and all your wires in the engine harness should still be hooked to the correct pins in their connectors to the UFB and the PCM and at C100 connector. But in your first entry, you said you haven't modified your engine harness at all, then you say the harness you had made for the swap uses all the original connectors? What?
07-01-2007, 05:44 AM
#6
TECH Regular
Thread Starter
Join Date: May 2005
Location: Bay Area, CA
Posts: 406
Likes: 0
Received 0 Likes
on
0 Posts
It works! Blows cold. Hopefully it holds its charge and the compressors seals aren't shot. Bought all the tools and all. Kind of a fun/interesting thing to do.
Eagle - the engine harness is all stock. The plugs that meet the engine harness only have the wires needed to make it a standalone system, I didn't use the stock UFB.
Eagle - the engine harness is all stock. The plugs that meet the engine harness only have the wires needed to make it a standalone system, I didn't use the stock UFB.
