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Yet another summer AC question/confusion by da.slyboy
Started on: 07-21-2014 11:16 AM
Replies: 5 (336 views)
Last post by: da.slyboy on 07-25-2014 09:53 PM
da.slyboy
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Report this Post07-21-2014 11:16 AM Click Here to See the Profile for da.slyboyClick Here to Email da.slyboySend a Private Message to da.slyboyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Car is a 86 4 cyl, v5 compressor.

Starting with a little history, the PO at one point in time removed the compressor and the compressor brackets ;( . I found the AC power relay on the LH side of the engine bay had been removed and a hair pin had been used to jump power to the dark green compressor power wire. The compressor power and both high and low pressure connections had all been melted due to excess heat or laying too close to the exhaust. I replaced all connections and wired them to what I thought was the correct locations (both high/low connections had green and white/red strip wires). Also replace the ac power relay.

I bought a new V5 compressor, found the brackets, bought a new engine compartment connection hose, flushed the system, replaced all o-rings for r134a conversion. I hooked up a set of manifold gauges and pulled a vacuum for about 45 minutes. After letting the system set for a few hours to confirm vacuum was holding I proceeded to fill the system. After adding a 12 oz can of r134 I noticed the low side pressure rising to 60 psi, high side was around 50 and my compressor wasn't kicking on. To confirm my readings I rented a second manifold gauge from autozone. As I started to add a second 12 oz can, the low pressure was steadily climbing but the ac compressor was still not activating the clutch. While I'm not the foremost expert on auto ac, I believe a fully empty fiero ac system should hold around 32 oz of r134a. This leads me to believe that the compressor should a least attempt to kick on with 18 oz of coolant correct? At least I thought the low side pressure would be high enough to activate the clutch coil ( 65 psi at 80F outside temp).

To confirm the compressor was at least working, I borrowed the PO method and removed the AC relay and jumped the power. The ac clutch kicked in and pulled the low side pressures down to 30, high side stayed around 55-60. I kept the compressor running until I emptied the second can. I have cool air blowing through the vents. However, as the can emptied the low side pressure was rising slowly back up to 50 psi (high side still only at 55-60). Now I believe I still need to add at least 10 oz of r134a from many of the articles I read. I've also learned that my low side pressures should be lower and my high sides higher. Complicated with the fact that I believe I"m by-passing the high/low switches on the back of the compressor but jumping the ac relay power, I'm hesitant to add more until I can get the compressor to run on it's own.

So I guess my question is how should I go about testing to see if the high/low switches are working, and if the ECM is reading it? Should I finish filling the system to recommended capacity and then recheck pressures? What pressures are needed to activate the compressor? Where do the LT blue/blue wires at the ac relay go? Why cannot the weather be 75 degrees year round
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josef644
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Report this Post07-21-2014 12:09 PM Click Here to See the Profile for josef644Click Here to Email josef644Send a Private Message to josef644Edit/Delete MessageReply w/QuoteDirect Link to This Post
The ECM grounds that relay which engages the clutch. I bypassed the ECM and made a permanent ground to the chassis. My ECM was out of a non AC car. Just try grounding the relay with a piece of wire and see if that makes the compressor come on. If good, then you will know which direction to go from there.

[This message has been edited by josef644 (edited 07-21-2014).]

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da.slyboy
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Report this Post07-23-2014 09:49 AM Click Here to See the Profile for da.slyboyClick Here to Email da.slyboySend a Private Message to da.slyboyEdit/Delete MessageReply w/QuoteDirect Link to This Post
I tried grounding the relay but with no success. Upon further inspection and research, I believe I should have 12 v to the lt blue wire with ignition turned on and ac selected. But I do not. Is this 12 v supplied by the ecm or the head selector?
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Report this Post07-23-2014 12:25 PM Click Here to See the Profile for josef644Click Here to Email josef644Send a Private Message to josef644Edit/Delete MessageReply w/QuoteDirect Link to This Post
The control head furnishes 12V to the low side switch, high side switch,then to the AC compressor control relay 'A'.

'C' is then grounded by the ECM energizing the relay.

+12V from the 25A fuse to AC power relay to 'E' on the compressor control relay out to 'B' to the compressor.

"A' 'B' 'C' 'E are the sockets on the AC compressor control relay.

Diagrams are on pages 63-6 and 63-7 in the 86 Factory Service Manuel. Read this section FSM 63 as it will tell you how to troubleshoot the AC electrics.

Good luck

[This message has been edited by josef644 (edited 07-23-2014).]

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da.slyboy
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Report this Post07-25-2014 09:51 PM Click Here to See the Profile for da.slyboyClick Here to Email da.slyboySend a Private Message to da.slyboyEdit/Delete MessageReply w/QuoteDirect Link to This Post
So I found part of my problem. From reading other threads I decided to check my control head for melted ribbens on the circuit. Sure enough there was and the reason I didn't obtain 12V to the green wire on the low pressure switch. Just for system testing, I jumped the low pressure switch and BAM my clutch activated. Excited I continued to fill the system with the proper amount of 134a from a empty system (approx 32 oz). When completed I was getting cool air from my AC (yea). As I put things away I found that I still had low pressure switch off the compressor and jumped. When I unjumped it and plugged it back in and tested.....I was back to square one. The compressor would not kick on. Static pressures with engine off (and running) were around 90psi which I would think would be more than enough to trigger the switch. Could I have placed the switch on the wrong port? These are new switches with the high side color coded blue and low side color coded purple. Is there anything else I'm missing? I surely didn't put in a bad switch did I?
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da.slyboy
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Report this Post07-25-2014 09:53 PM Click Here to See the Profile for da.slyboyClick Here to Email da.slyboySend a Private Message to da.slyboyEdit/Delete MessageReply w/QuoteDirect Link to This Post

da.slyboy

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Member since Dec 2012
Oh and the high pressure switch (blue) is currently on the bottom half of the compressor and the low side (purple) is on the upper half.
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