anthology1987

so here's the deal; after switching out some sensors the other day i reset the ECU by disconnecting the battery. when reconnected i blew a couple fuses and now the AC compressor doesnt engage. i took it to the shop (where i recently had the AC done) and they said it had to be electric, i wasnt charged a dime which is cool. so i took her home read through the service manual available on the FAQ pages.

what i found; the relay, pressure switch, thermostat and all other components are working. when i turn on the AC the BAC increases the idle, so obviously a signal is getting through the relay and the pressure switch making the ECU is give the "ok". So then i decided to trace the wire that engages the AC clutch and test it at every connection all the way back to the logicon and decided to put a 12v connection to the wire (after taking it out of the connecter) and sure enough the compressor engaged. so now knowing that the logicon just isnt getting the signal out and with no signs of fried diodes, resistors, solder joints and etc i've decided to simply install a switch for engaging the compressor seeing how all other conditions for the AC system are being met.

what i need is for someone to simply find out exactly how many volts are going through the wire that goes to the AC compressor, just to be sure i dont fry anything by just assuming its a steady 12v. an easy place to test this is at the AC relay, test the black with a white stripe wire as pointed out below:




for those who dont know, there are two round shaped relays at the very front of the car on the driver's side, the AC relay should be the left one.

sorry for typing so much.

jackhild59

iTrader: (7)

This a very bad idea. If you do this..

The compressor won't cycle on low pressure; then at some point you can actually pull a vacuum on the low side. very bad sucks in the bad stuff-air, moisture etc.

The compressor won't cycle on low evap temperature; then the evaporator will freeze up into a block of ice-no airflow OR cooling

The compressor won't cut out on high pressure. BLAM!!!!

Have you checked your ROOM fuse? That will keep the A/C from working...

Good Luck.

HAILERS

I didn't check with a meter, but the power to the clutch comes from A1 as seen in the wiring diagrams and that's from a acc fuse. So it's batt voltage/alt voltgage.

You getting any power to the R/Y wire at the relay?? Got a gnd on the L/W?

anthology1987

an alternating current to control cycles... i never knew or would have thought of that. dam! thanks for tellin me.

ive tested all fuses, everything should be ready to go. i even replaced the room fuse because it was blown, but that was the other day and its still not doin it.
when i lost AC, radio and dome lights, i replaced the room fuse and all came back except for AC.

and yes im getting power at the R/Y wire going to the relay, i believe thats whats turning the relay on. i've followed every wire involved to look for loose connections and found nothing

and i know thermostat and pressure switch arer working cause when i disconect either terminal at the pressure switch my ECU stops the idle compensation so there must some communication goin on there.

im stumped! but ill keep trying to find more info and test more things. i hope i dont end up having to pay the mechanic to find and fix.

HAILERS

So your getting the power to the a/c relays coiil. That's nice. Are you getting the ground signal to the relays coil from the ECU?? Or not? L/W wire.

anthology1987

all i have is a wire prod with a light to test. i lost my ohm meter. when using the prod im not getting anything from the L/W wire. correct me if im wrong, should i be able see the light when touching the L/W connection or do i really need that ohm meter?

this is my first time ever reading an eletrical diagram and messing with relays and switches. yeah sure i've taken pannels and control units appart and have had to resolder connections, but trying to understand how the AC system and this diagram works is somethin else.

HAILERS

Turn the A/C on.

Get a piece of elect wire and strip each end of that wire.

Go to the a/c relay and with the electrical plug attached to the relay......put one end of the new wire to a known gnd point. Put the other end of that new wire into the backside of the L/W or blue/white wire where it enters the elec plug. The relay should pull in IF the R/Y wire has power on it.

anthology1987

i did it and nothing happened. i do have power at the R/Y wire and believe that L/W is grounding seeing how the relay clicks on, but there is no power on the wires leading in or out for the compressor.

you were saying earlier that the power for the compressor comes from A1, but what is the diagram trying to depict when it shows the L/B wire coming from the A1 connection then spliting off, going to the relay and going to the logicon. what exactly is going on there?

HAILERS

L/B should have power on it with the key ON. It gets fed by one of the ACC fuses on the bottom row of the interior fuse box. Look at a series five fuse box cover and see which one.

If the battery has been run down a lot, the relay may pull in/click, but there won't be enough power to make the clutch pull in. Start the engine. IF the engine will start.......then that is not the problem.

See jpg for the fuse on the bottom.

Go to the diagram I posted in an earlier post. See how the L/B wire goes from the relay to the top of the page where you see a black line with ( A1)???? The A stands for accessory buss. So now you go to the wiring diagrams in the front of the wiring book and find the page that shows the fuse box. You find the (A) line and follow it down to the fuse box where it has the (1) and there you find a 10a fuse with a L/B wire going into it.

IN other words its the 10a fuse on the bottom row of fuses in the interior. This is for series four. Series five might be a bit different.

You have shown that the gnd on the L/W will pull the relay in, so it does make sense to find out if the L/B has power on it ..........or not.

anthology1987

I'm gonna pull each fuse and test each one, cause visibly all fuses are good and actually I think I put a 30 for the room so ill be changing that back to a 7.5, but I won't be able to do this till I leave school. I should have it done by 2 and we'll see if that'll fix it.

Probably a stoopid question, but is the s5 fuse pannel the same as s4?

----------------------------------------------------------------

I didn't even think of looking at the wiring @ the fuse box and didn't really know where A1 lead to, so thank you for opening my eyes to that. Ill check all that when I get home and get back to you.

Thanks for all ur help man!

HAILERS

Series five fuse box cover is shown in the FAQ thread.

The relay pulled in. If the relay pulled in, then for some reason the L/B wire isn't powering the a/c clutch. The problem HAS to be with the L/B fuse or???? but L/B related.

The interior fuse box has several BUSSES. One buss is the battery buss and has power on it day and night.

The ACC buss has your a/c power and has power only if the key is to ON or the key is in ACC.

The IG1 buss has power only if the key is ON or in START.

The IG2 buss has power only if the key is left in ON. It has no pwr in ACC or START.

Stare at the fuse box in the right hand corner of the LAST jpg I attached above and you'll see ACC......IG1...........IG2.......B........written under the fuse rows that are applicable.

If you understand how the fuse box fuse rows get power from the key/BTN fuse...........then you can fix electrical problems much easier. Much easier.

LIke if the batt is being drained down with the key out of the car and igniton in OFF, then the power draw cannot be from a fuse on ACC or IG1 or IG2..................UNLESS someone monkey fucked up the wiring from stock. Then there's no hope at all so sell the car at that point. Monkey **** come out of a squirrel installing a radio or some aftermarket electrical. humor, please.


I wrote all the above thinking this was a series FOUR car. A series five is similar if you look at the attached series five diagram. CIGAR fuse actually powers the clutch thru the relay. The relay gets pulled in by other means already mentioned i.e gnd on the L/W from the ECU and power from???? either WIPER or ROOM .........or METER.....depends. Series five uses two differnt schematics for two different ways of wiring the thing. See the several series five wiring diagrams if you have a series five car.

anthology1987

Wow I feel f-n stoopid making things harder than they have to be! Lol

It was a fuse, I guess I'm blind and couldn't see it was blown and wouldn't u know that after replacing it everything works.

Thank you for stickn through and helping man, ur the best!

HAILERS

I need to correct something that I wrote that is wrong. I said to check for a gnd being put on the L/W wire of the relays elec plug. Not the way to do that. With the A/C OFF, the L/W should read batt voltage. With the A/C ON, the L/W should read less than two volts dc.

IF everything now works........great.