A/C troubleshooting

[Briano1234]

F14 is the main fan fuse, for positions 1,2,and 3, 4th position by-passes, so you may have a bad ground lead on your blower motor, look under the drivers side knee bar for a 5 pin mylar connector that goes up to the heater blower. I have had 3 cars that the ground wire got toasty hot to actually become open.


If you used the 2 red covered wires from the right side of the a/c controls, then they are correct to start and stop the a/c.
If you used a lighted switch, then take the ground off he switch as you are going to blow a fuse. If the fan doesn't come on as the fuse is blown, the
a/c compressor won't cycle.

So you are going to have to de-bug the wiring. I don't think your pressure switch is bad, I think you are just jumpering it to eliminate the other crap that is the issue.

I have only seen one a/c relay go bad, and that is over 30 years of driving. It could be bad, but just saying you have other issues if you are blowing that f14 with no f14 the main part of the a/c relay can't pick to energize the rest of the a/c system.

[GreenCabbie]

Ok I'll see if I can find a short to the No.14 main fuse . And the 5 pn mylar connector. Does this connector connect to the blower directly or to another connector.


When I look in the relay area and unscrew the screw that holds the fuse and relay block and pull the entire wire , relay, and fuse holders to me . I can see where someone tried to splice two wires together with a wire splicer. But only one wire is in the wire splicer. It is a yellow color with a red tracer, it is the only wire in the blue wrap around splicer. I have looked for other wires in the area that have cut marks on them that may have fallen out but it is not clear to me. When I look at the wiring diagram for air conditioning I don't see a yellow wire with a red tracer used. Any ideas on what this is?

I also checked the low pressure ac refrigerant switch NC with my multimeter and it was ok as well as the high pressure ac refrigerant switch NO. I understand now the difference between the a/c compressor switch on the air distributor and the ac thermostat switch.

So by process of elimination. I'll focus on you 5 pin mylar connection.

As always thanks for the help

GreenCabbie

[GreenCabbie]

Well it's been a while since I posted anything. I am still working on trouble shooting my ac system. Briano is right. My problems seem to lie within my ac relay. I am at a loss as how to trouble shoot the relay. Any help would be appreciated.

One thing I did was find a corroded 40 Amp overcurrent relay next to the battery that was a total waste. Covered with corrosion. One of the sets of wires was just hangin there. So I ordered a new one. And installed it. I don't see this relay on any of the wiring diagrams and it is baffling to me how it was connected. The 30 Amp fuse shown on the wiring diagrams on line 4 is not in this car. I am thinking this is the replacement.

There is a 10 gage red wire that has 12 vdc on it when everything is off as long as the 30 amp fuse on the fuse block is good. I blew the fuse once to discover this. Which makes me wonder because the wiring diagram on line 4 shows this relay should be directly connected to the battery.

There is another red 10 gage wire that is joined with the one mentioned above that runs the fan. On the other side of this set of contacts is a red and white wire that goes to the ac relay. I toned it out to be sure.

The wires that activate the contacts for this 40 amp overcurrent relay are two red/ black wires 14 gage that have no voltage on them. When I turn on the fan selector switch I get no voltage on these two wires. When I start the car nothing happens with them. It is really hard to trace these red/black wires as they go into the black cover of wires and from there I don't know where they go. So I don't know what really activates them.


All I have checked leads me back to the ac relay. The relay doesn't seem to be outputting anything.
I can't tell if the voltage going in is doing anything to this relay.
I have three of these ac relays. I have tried them all and nothing changes. I don't think all of these relays would be bad.

I even tried bypassing the ac thermostat and the low pressure switch to see if the compressor clutch would engage. No Luck. Must not be any output from H4 on the ac relay output.

I have opened wire connector T5b and applied 12 vdc directly to the high speed of the fan and it worked so I know the high speed of the fan works it again points me to the ac relay connection H6.

Between the overcurrent relay red/ black wires mystery and the ac relay relay mystery I am bewildered.
But determined to get to the bottom of this. Thanks for any advice.

[Briano1234]

The relay that is on the Fender is for the fan, and the after fan run circuit.
So if you apply 12V to the Supply side of the low pressure switch, there are 2 green wires one goes to the compressor, does the compressor pick?
Yes. Compressor clutch good, low pressure switch good.

No, then apply 12V directly to the compressor green wire, if the compressor engages then you have a problem with the Low pressure switch, or no Gas int he system.

When you turn on the car key to the run mode, and turn the vent selector to a blue area, then turn on the blower fan, does the Radiator Fan come on?
Yes, do you also hear the compressor pick? no to the second part leads me to the relay or the thermofuse. ( that is actually a breaker).

No, then you need to fix the fan circuit.
have you taken the thermofuse out and verified that it is good with a meter?

[GreenCabbie]

Well I am still working on my ac system. Problems I have are; 1. I can't get the compressor clutch to come on. 2. I can't get the fan to work in the high speed.

I have been trying to locate the problem and as Briano suggested I think it is in the ac relay. I have jumped pass the ac thermostat switch (line 7 on the wiring diagram)and the low pressure switch ( line 6 )and still the clutch doesn't come on.

One additional discovery is I found a highly corroded 40 Amp CB relay by the battery. The wires literally were so corroded they were not connected. So I ordered a new one on ebay and installed it the same way it was hooked up when I found it. My problem is I can't make sense of the way it was installed.
The wiring diagram doesn't show a 40 A CB relay. Only a 30 Amp fuse. So a previous owner must have made some modifcations to this area of the car.
There is a 10 gage red wire that has a 12 vdc charge on it all the time and is connected to one side of the NO contacts. Joined to this wire is another 10 gage wire that is not hot and goes to the fan circuit. On the other side of the NO contact is a red/ white wire that goes to the ac relay.
The wires that activate the NO contact are two red/ black wires 14 gage that I don't know where they go?
They don't have 12 vdc on them when I turn on the fan or run the engine. So I don't know where they go or what activates them. They aren't activating the 40 A CB relay.

How would I trace these activation wires down?

I have checked the outputs at wire connectors T5a and T5b and it just confirms in my mind the ac relay is not working properly. I have 3 of these ac relays and have tried them all to no avail.

How would I check the 12 vdc input to the ac relay? I don't think the relay is getting any power based on the outputs that it should have?

Anyhow I am really scratching my head about these two items . A non working ac relay and this 40 A CB near the battery. Any help or troubleshooting ideas would be appreciated.

[Briano1234]

The fan not working hi-speed, is that relay on the fender.

Blower fan not working on "high" is the a/c relay.

E/35 a/c switch (blue slider on heater controls) make the connection in any blue or defrost position.
Once it is closed then it allows ground to go through the motor to pick the a/c relay picking coil which when 3/3 picks it also energized 2/2, and 4/4.
This then closes the switches in the relay placing power from F23 on to the pins 7/7 pins 6/6.

with 7/7 and 6/6 closed current with no resistance can then run the blower fan at high speed through 6/6.

the Pick at 3/3 caused the 6/6 to be hot and also energizes 2/2 further.

7/7 closing allow a current path through the compressor.

4/4 contact allows current to go through the Fan motor "hi" side.

Now when looking at the schematics for the a/c, on the radiator fan you also have to refer to the non-a/c apges
as that is where the red/white are coming it to the relay to power it.

so Both relays are needed.
Hope it is a little clearer than mud now.

[GreenCabbie]

My mistake for sending msgs that were somewhat duplicate. So I will
clarify here.

I did apply 12v to the supply side of the LPS and the clutch came on! So your note said clutch and LPS are good. Yahoo!

Plugging the supply green wire into the supply side without a 12 v jumper clutch does not engage.

Next question was when you turn on the car key to the run mode, I assume this means with the car started. And turn the vent selector to a blue area, then turn on the blower fan does the radiator fan come on. Answer Yes it does. Clutch on compressor does not pick up?

I have taken the thermofuse out since it blew and replaced it with a normal fuse. I could not find the replacement thermofuse at Autozone. Is it important to have a thermofuse?

I do follow you on explaining how the relay works with a little muddy water which is very helpful. My question is I don't think E35 a/c switch is activating the relay at 3/3 ,2/2 and 4/4 that then doesn't operate the contacts at 7/7 to turn on my compressor and 6/6 that would run my blower fan in hi if I had the blower fan selector switch in hi.

How do I check this E35 a/c switch input ? I quess I could pull off the plug into the a/c relay and check for continuity first. Looks like a r/bk wire coming into the ac plug. Or jumper around it to see if the a/c relay does pickup?


I appreciate the clue on J26 Radiator cooling fan relay. Cleared up a alot for me. I do have a R/W wire that isn't shown on my wiring diagram and was connected to the opposite side of the contacts and red wires coming from the S1 30 A fuse. My book shows a r/bk wire in that location.

What is line 31 in the upper part of the wiring diagram page indicate? I wonder where it goes and if it could be part of the problem since it looks like it comes in at the same point E35 a c switch ( blue slider) connects into the ac relay. I am just guessing here trying to be thorough.

To summarize my rambling ,here are my questions; Is a thermal fuse the same as a normal fuse?, How do I check the E 35 ac switch input to ensure the relay is getting power? Is the R/W wire on the J26 radiator coolong fan relay the same as shown in my wiring diagram as a r/bk? What is line 31 above where the power connections are?

Thanks Briano for your help.

[Briano1234]

I have taken the thermofuse out since it blew and replaced it with a normal fuse. I could not find the replacement thermofuse at Autozone. Is it important to have a thermofuse?

YES, a Thermo fuse takes more current, and some places they are called breakers, that will reset with they "pop" Think of the circuit breakers in your house, except they auto reset.

E-35 is the white switch that is on the passenger side of your heater selector. It is functioning if the blower fan is on. That is if you slide your a/c-vent slider to a black area except defrost, the fan for the radiator doesn't come on. (key in the run position).

Now, as we look, we see that the a/c relay is half-assed working. But there is the a/c thermostat, that you havn't tested yet....
So it is before the Low pressure switch....

Where is it located? I Know, I know, I know........ It is on your heater controls, left side of the controls bottom. It has a mercury tube that extends down to the right side of the heater box in to a tube that runs in front of the a/c Evaporator (Actually is affixed to the evap.). The purpose of this is that if your Evaporator is covered with lots of frost as in ices up, then it shuts off the compressor to allow it to defrost, then turns it back on when the evaporator is frost free...This is why cars drip water out the bottom when they are running a/c.

Since you know that the voltage is missing at the low pressure switch, then this switch or the wiring from it is now where you need to concentrate.

Getting to that switch means that you have to remove your fascia. and the controller. Then flip it over, as there is a wire tie at the back of the control unit that holds the fan switch wires on it and you may have to cut that wire-tie. BE VERY CAREFUL as that Merc Tube is Eye-taliban for FRAGIL'e. it will bend a bit before it breaks, but it don't like to be bent to hell..then tried to straighten.....

On my old Diesel Rabbit I did have that switch go out on me, but it caused the a/c to run forever.... So I suppose that the wires from it could of broken, or that the switch is bad.

If you measure 12V at that switch on one side but the other, then that switch is bad. If there is not 12V on either side then your a/c relay is bad at pin 7/7

Since you said that you have replaced the relay, then I would lean to that switch or the wires to it as bad....
You can jumper that switch out, and the Compressor should come on, and if it does then that switch is bad, if it don't then the relay or wire from it to that switch is bad.....

I have had that swing arm jump out of position and lock to the off, I used a washer under the arm on the switch to keep it more firmly in place.

I saw that listed at a parts place... but having a devil of a time trying to remember...

[GreenCabbie]

Thanks Briano,

I will go get a 30 amp thermofuse and install it. Trying to followup with your advice on the ac relay. I focused on the E35 ac switch. With the key on I turned the E35 switch to a blue position ,turned the blower fan on and checked the voltage to H2 on the relay by pulling the terminal plug off and using the H2 female plug to see if 12 vdc was there. It was. So I replugged the terminal plug expecting outputs from H4,H1, H6 but nothing. So I know I am getting 12 v to the 2/2 terminal on the ac relay just no outputs.

I have the ac thrmst E33 jumped so if I had 12v coming out of H4 when I had the car started the compressor should have come on. The compressor didn't so the only thing I can conclude is all 3 of my a/c/ relays are bad. Hard to believe.

I also thought about your idea ,it might be a ground wire problem. So I did some checking the only way I know to check ground wire problems is pull apart as many of the Brn wire connectors and check them against the grounding points on the firewall. They all toned out including the one in the battery compartment.

I wonder if I can check the fuse /relay panel internal circuits to see if the ground is not coming thru to the terminal 1 to activate the relay?????????? I can't see how to do this easily.

I also hooked up a 12 v supply to T5b2 , the high speed for blower fan and it worked. So I know the high speed works. It just has alot of crap in the way to get it going.


So to summarize my ramblings;
-I will get a 30 A thermofuse and install it.
-I have 12 vdc to H2 with the ignition on also E35 ac slider switch in a blue zone and the blower fan at 3rd speed but no other outputs to H6, H4,H1. Any ideas? Is it the grnd in the relay panel or a new a/c relay.
-Is there a way to check the ground wires better that I did?

Thanks for all the help, This has got to get easier sooner than later, I feel like I am chasing ghosts!
Greencabbie

[Briano1234]

H2 supplies the ground to the relay.
Since the Fan doesn't work in the 4th position
H3 should have 12V all the time.

Ok lets look at it a little different.

Ground which comes up from the bottom seeking 12v in Position 1,2,or 3 allows the Blower fan to come on which it does.
With the Fan on, there should be 12V or a potential at the h2 of the relay which you say there is. This should then allow 1/2
of the relay to have power and to pick and hold power for the 4th speed of the fan.
So that even with the a/c in the vent or heat (black area) there is still power to the 4th speed that is separate from the regular 1,2, or
3rd fan switch position.

Now when you turn on the a/c.

The fan switch on to position 1,2, or 3 applies a potential to the one side of the a/c switch as well as running the fan.
This applied potential will energize the a/c relay at h2, which you say you have, it may be less than 12V but real close
as it depends on which fan speed you choose.

Now what we know is that 1 the thermo fuse blew.

What does that mean?
That there was a direct short for a duration between Ground and the battery through that fuse.

Since you don't see a potential at h6, h4, and h1 It would appear to me that your relay is toast but wait there is more.
You need to verify that the wires from h1, h4 and h6 are not grounded.

What we do know is that s14 is good, and that s1 should be as s1 applies power to h1 if the relay half assed works.

So take the relay out lets test the thing outside of the circuit.
Lets test your Relay....... You may be able to use a fresh 9V battery to power the relay.... I didn't have one handy, so I used
my car battery....

You will need a DVOM (digital Volt Ohm Meter) and a three jumpers.

Pop the cover off the relay and look at it. Do all the contacts look good, and aren't burnt or stuck together?
Do all the soldered connectors look good




Lets look at it:


You will need 3 jumper wires.

Wire them up as in Pin 2 tied to Pin 3.
Now use +12v to pin 1.
Place Ground on Pin 2.

The relay should "click".

With your ohm meter you should have
Pin 4 to pin 5 @ 0 ohms.
Pin 6 to pin 8 @ 0 ohms.
Pin 7 to Pin 8 @ 0 ohms.
Pin 6 to pin 7 @ 0 ohms.

With the Jumper removed from pin 3
Pin 4 to 5 @ 0 ohms.
Pin 7 to 8 @ 0 ohms.
Pin 6 to 8 is open or infinite.

With the Jumper removed from pin2 and now on pin3
pin 6 to pin 8 @ 0 ohms.

Pin 4 to 5 is open or infinite.
Pin 8 to 7 is open or infinite.

Any thing else and your relay is toast.

You can open the relay by prying out the Phenolic from the case fingers

Look inside the cover is it rusty.... not looking too good here.

If you smack it on a table top do you get fine particles falling out?


You can try cleaning the corrosion out of it






You can even attempt to resolder it.




In this case the above truth table didn't hold as pin 6 to 8 to 7 had no continuity this was a spare relay that I picked up at a wrecking yard... and it rattled in my hand before I opened it.. So I knew it was probably toasted....

[GreenCabbie]

Thanks for all the info. This morning I put the relay thru the truth table and it passed. I was hoping it wouldn't so I could replace the relay and start putting it back together.

You mentioned that the I need to verify h1 , h4 and h6 are not grounded. How would I do that? Pull the plug off the relay and check to see if there is continuity to ground?

Also, I put 12 v on the blower fan hi speed circuit at T5b2 and the fan came on. So that tells me the problem is between there and relay.

I think I also have a problem at h3 with no power. Is there an easy way to check that? I have power at h2. Like you said varies based on the location of the blue slider E35 ac switch.

Any other ideas you might have on this would be appreciated.

Thanks for all your help,

GreenCabbie

[Briano1234]

You mentioned that the I need to verify h1 , h4 and h6 are not grounded. How would I do that? Pull the plug off the relay and check to see if there is continuity to ground?
Yes



I think I also have a problem at h3 with no power.

That is your problem.... No power from the fuse? no power to pic the 4th speed on the fan as well as power to the a/c compressor.
With the Fuse removed Key on, you should have 12v on one side Nothing on the other.
With the Fuse in, and the a/c on you shoudl see power on both sides.

Did you Measure your fuse with an Ohm Meter?

[GreenCabbie]

You are on it. I just checked the power to H3 from the S23 fuse . No power on either side.
I turn the key on and I still get no power.
How the am I going to find where this wire is grounded? I lose the supply side red wire when it disappears into the wire bundles. Does it go all the way to the battery by itself or is it tied to other red wires coming from the battery. I did test it for continuity with positive battery cable disconnected to see if it would tone and it did.
So I assume it is connected just grounded somewhere? Correct?

I also thought it would be a good idea to see if I had any amps going to ground. So I disconnected the negative terminal battery cable put my multi meter on dc amps and measured 4.3 Amps going to ground. I have memory in my radio but that seemed like a lot of amps.

I will measure my 30 A fuse with an ohm meter but I will be getting a new 30A thermofuse tomorrow to install as well.

Any ideas on how to trace the red power wire to the s23 fuse the easiest way? I only see bundles of wire I will have to tear apart until I find it?

Thanks again for the help,

GreenCabbie

[Briano1234]

Whoa wait.......

Remove the Fuse, do you have 12V on one side or the other? Yes, issue between the fuse non-12V side and h3 on the relay socket.
No 12V on either side of the fuse is a bad wire from the fuse back to the battery.

With the Fuse removed, measure resistance between both sides of the fuse to h3 the side that isn't a direct short as 0 resistance is good, it is the other side that is going back to the battery that you are having issues with.

That Thermofuse, isn't grounded. A Fuse prevents over current from damaging wires if something shorts out.

Definitions.

SHORT: A direct path to ground.
OPEN: A circuit that is devoid of a path to either b+(+12v in a car) or to ground.

Fuses: Are Current Limiters, that allow a certain amount of current to pass before they expire.
A direct short to ground causes the Fuse to get really excited, and shat itself. So a Fuse Opens up, after the Short occurs.

In a Circuit Current flows and Voltage is felt at any given point.
Think of Current as water in the river, and Voltage as checking the Depth at any one given spot.
(Yes I do Electronics..I am only a mechanic by choice..)

Basic electrical primer: viewtopic.php?f=11&t=2847

The Thermofuse on one side goes straight back to the battery.
The other side goes to the relay as h3.

If there is not 12V on either side of the fuse, then you have a broken wire from that one side of the fuse straight back to the battery.

Look around your battery for a spare red wire about 14 gauge, it should be hanging off the Positive cable area. It could be that someone forgot to
reattach it. Otherwise you are going to have to track that sucker down. Since the Bentley dosen't refer to it as having a connection number to the fuse box, then it is one of the additional fuse holders. So it should be a free connector...... You will need to track it down. Once you have 12V to one side, then I think baring any other shorts you have found your answer. It may be easier to find the wire that goes in to the fuse box for h3 on the relay, then cut a new wire in that goes back to the battery on the other side.

So replace the fuse with another Thermofuse and give it a try.....

[GreenCabbie]

Good news yesterday the Hi Speed Blower fan came on and the clutch on the compressor. I installed another wire from the supply side of the S23 fuse to the battery and it worked. Really I jumpered around the outside of the car to see if it would work and it did.

So now I need to install it thru the wiring tubes. That doesn't look easy. Any ideas on how best to do this without cutting the wire tubes to pieces. I was going to try to pull the new wire in as I pull the old wire out???

At least I know that is the solution. Thanks for pointing it out. I would have never thought the power wire to S23 was the problem.

Now I can put it all back together including the compressor on off switch which didn't work before but should work now. And give the cool air I didn't get before.

Anyhow Thanks for all your help and coaching,

GreenCabbie