blehbleh

So my 97 maxima has relay coil power (terminals 1 and 2) of 13 volts when the A/C button inside the vehicle is pressed, but the compressor doesn't turn on. It only turns on if I jump the power wires (terminals 3 and 1 or 5). What gives? The relay should be switching the circuits to on...but it isn't...

plugeye

probable cause=freon is too low.

njmaxseltd

iTrader: (19)

+1 Low refrigerant will trip the low pressure switch and interrupt the signal to the clutch.

blehbleh

oh shoot, I forgot to say I fully recharged it, vacuum and all...

blehbleh

Cause the pressure switch wouldn't switch and the relay wouldn't get power if the switch detected low refrigerant

pmohr

iTrader: (26)

You'll always have power on pin 1, it's fed directly from the 7.5a 'AIR CON' fuse in the interior fuse box. Do you have ground on pin 2 from the ECM?

If you're getting proper ground control at the relay and it's not switching, you need a relay. Swap it out with a similar relay (anything that's the same color, the horn relays, fog lights, etc). and see what happens.

blehbleh

I've already swapped relays and tested them with the fog light relay circuit.

I've put a multimeter to pins 1 and 2 and received 13 volts when the A/C button was pressed, so I assume there's ground on pin 2.

I've tested pin 12 on the ECM and it has proper battery voltage.

I assume if the switching circuit has proper voltage, shouldn't the charging circuit for the compressor turn on?

pmohr

iTrader: (26)

You should not have battery voltage at the ECM at pin 12 (ACRLY) if it's requesting AC function, that should be pulled down to ground. If the ECM has B+ at pin 12, then you don't have ground at pin 2 of the relay.

Plug the relay in and recheck your measurements in reference to ground (so the circuit is under load), it's possible there's corrosion in one of the connectors or wires between the ECM and relay, and you're getting a large voltage drop.

Unplug the ECM, provide a ground to pin 12, see if the relay activates.

blehbleh

oops, I meant pin 21. This is in regards to the diagnostic procedure in the manual.

blehbleh

I re-read the diagnostic procedure and it states that pin 12 should be ground and receive 12 volts...

"Do approx. 12 volts exist between ECM harness 12 and body ground?"

If yes, go to 2 of 3.

blehbleh

lol, I didn't read your whole post...I didn't check it with a/c button on...I guess I'll do that...but isn't it technically checked out if I test the relay terminals instead?

blehbleh

so I noticed the when the relay is connected and tested with a multimeter at the terminals of the relay voltage is only .02 volts...without the relay connected and the multimeter directed connected into the circuit (1 and 2 terminals) it's 13+ volts...

I then tested to see if the relays are supposed to be like that...nope...at least not for the front fogs..

What is going on?

I tested the a/c relay with the battery (same voltage as the relay coil circuit) and it clicks...

blehbleh

i'm thinking there's a short in the system for anyone interested. Once the trigger circuit completes something else steals it's power. I don't know the function of the multi meter, but I don't think it completes a circuit when it measures voltage, hence which it reads correct voltage.

pmohr

iTrader: (26)

This is a perfect example of why circuits should be tested under load, and not statically. What you're seeing is a voltage drop due to a poor connection somewhere, be it corroded terminals or a loose harness connector.

First thing to check is terminal tension at the AIR CON fuse in the interior fuse box, make sure the fuse doesn't just fall out, that it's a decently tight fit for the blades of the fuse. Also of course you're checking for corrosion, or a questionable fuse. Next I'd be looking at the harness connectors behind the fuse box for the same thing, corrosion or damaged terminals. Do the same all the way up to the relay itself.

It's not a short, it's closer to an open circuit.

If the meter didn't complete the circuit, it wouldn't be able to read voltage potential.

blehbleh

ok...but if it was an open circuit how does battery voltage register at the coil relay terminals 1 and 2?

i've jumped relay terminal 2 and terminal 1 on the a/c pressure switch and the clutch engaged. Is it possible the ground connector on the pressure switch connector completed the circuit? Possibly.

I know inbetween the relay and pressure switch is the ecm...i've tested continuity between the relay and ecm terminal 12, good to go. I've also tested continuity between ecm terminal 21 and terminal 1 on the a/c switch...good as well. Lastly, terminal 13 from the a/c button and a/c pressure switch terminal 4 there's continuity.

So that tells me that from the button to the pressure switch wiring is good. From the switch to the ecm wiring is good and from the ecm to the relay terminal wiring is good. That's the whole relay coil circuit if I'm not mistaken. Could it be the pressure switch? I don't think so because like I previously stated if I back probe terminal 1 and connect it to the a/c relay 2, which eliminates the ecm, the clutch engages.

If I jump terminal 3 and 5 on the a/c relay the clutch engages. This tells me the connection from the battery to terminal 5 on the relay is good.

I see in a wiring diagram the ignition switch has a fuse that's also connected to the circuit...is this the 30 amp fuse?

If terminals 1 and 4 on the pressure switch connector are jumped is it supposed to engage the a/c clutch?

pmohr

iTrader: (26)

Not an open circuit, I said closer to. Voltage drop is, more or less, closer to an open circuit than a short circuit. You should be dropping full battery voltage across that coil.

All you're doing when you connect pin 1 on the triple pressure switch to pin 2 on the relay is providing a ground path to the coil that the ECM or the wiring to the ECM is apparently not sufficiently able to.

It's not an ignition switch fuse, it's just a switched (and of course fused) power supply to the relay coil. No, it's not 30a, where'd you get that number? As I said above, it's a 7.5a fuse.

Again, you're measuring the circuit at rest. Notice how before you noticed nothing wrong until the circuit was loaded? That's the point of testing a live circuit. A static ohm check is useless for wiring except for seeing if a circuit is completely open, it isn't loaded enough with the typical 500mv and extremely low current flow.

As I said above, disconnect the ECM, apply a ground to pin 12, see if the relay activates. That will prove out your wiring and connections from the ECM to the relay much more than a simple resistance check will. You have two paths to take from there, but we won't know what to do until you do as I've asked.

And no, jumping pins 1 and 4 on the triple pressure switch is the same as having refrigerant pressure too low to trip the switch; those terminals are connected at rest.

blehbleh

so basically you want to see if ground within the ecu is working correctly? I did realize that connecting pin 4 to relay pin 2 provided ground...

pmohr

iTrader: (26)

Yes.

blehbleh

Ok, I've tested the relay 2 to ecm wire via grounding terminal 12 and the relay works.

So at this point what choices do I have. Is it possible the ground on the ecm is bad? Or is that unrelated and the ground circuit is separate and controlled otherwise?

pmohr

iTrader: (26)

It's possible there's a bad ground to the ECM, or a failed driver internally. Check all your grounds, pins 10, 19, 25, 32, 108, 116 and 124.

Negative voltmeter probe to ground, positive to each of those pins, with the car running.

They all go to the two ground cables on the lower intake manifold, it's a good idea to clean those up regardless.

blehbleh

So what's the function of the a/c driver specifically? If I were to wire a wire to the pressure switch from the relay would the compressor still turn off when pressure is achieved?

I hooked up a manifold gauge with the compressor on and the high pressure line has only around 50-60 psi...but the air still blows cold.

blehbleh

I forgot to mention I've refilled the refrigerant via an exchanger, so that's all fresh.

blehbleh

So am I supposed to check for continuity or actual voltage?

Voltage is like .09...supposedly it should be ground voltage...

I didn't get any continuity from pin 10 and I assume the others, didn't check, while the engine is running. I did get continuity from all with the engine off though.

njmaxseltd

iTrader: (19)

You don't have enough refrigerant in the system. How did you charge it? There's no way you would have blown cold air with only 50-60 psi on the high side. You need to be around 200 psi on the high side and about 25 psi on the low at approximately 70 degrees outside temp.

Take your volt meter set to ohms and measure the low pressure switch. I guarantee is show's open which is why the compressor isn't running.

pmohr

iTrader: (26)

Voltmeter == voltage. Ohmmeter == ohms.

Voltage, not continuity.

Why would you check one and assume a reading for the others?

Again, all this is assuming you actually are getting a ground path from the ECM to the relay, but it's not able to energize the coil. I've been skimming over everything else since you said you were reading a ground at the relay itself.

njmax is right, how much refrigerant did you charge with? 60 PSI is nowhere near enough on the high side.

blehbleh

1.45 lbs, vacuum pulled and all.

At the relay it was registering ground...

Ya, I'm not sure how it's blowin cold, but it is. That pressure was read with the compressor jumped.

Thing is, the pressure switch was the first thing I did as far as fixing is concerned.

blehbleh

with a/c button push on continuity between terminal 1 and 4 exist...none when button is pushed off. Positive to 1 and negative to 4.

blehbleh

I apologize, I swapped the leads opposite. They're good.

blehbleh

I think I omitted some info hoping it wasn't the problem, but I was welding the 12mm transmission drain plug bolt because it stripped and found out the abs computer fried. I replaced it, but I suspect the ecm was damaged as well.

blehbleh

sorry for wasting your time...

Definitely thanks for the help...very knowledgeable individuals.

njmaxseltd

iTrader: (19)

Huh? Did a fix it? Your not wasting anybody's time, we're trying to help you.

blehbleh

Not sure yet, I have a used ecu on order...pretty cheap too.

njmaxseltd

iTrader: (19)

The ECU has nothing to do with your pressure issue. If you indeed measured on 60 psi on the high side with the compressor jumped and running, you don't have enough 4134 in the system. Check the low pressure switch for continuity.

blehbleh

Ya, I know. Thing is, it was evacuated, vacuumed and refilled properly.

Anyhow, I replaced the ecu and the clutch turns on now.