jmille25

I have a 2004 EX that I recently purchased and the A/C does not work. When I press the A/C button, the RPM's do not increase nor do the fans come on. Fuses are ok, relays are ok, and A/C pressure is ok. The previous owner said he had replaced the heater control panel, but it did not fix the problem. If I use a jumper wire, I can get the A/C clutch to engage and get either fan to come on.

If anyone has any ideas with regards to what I could try to do to narrow down the problem, the help would be greatly appreciated.

ezone

Sounds like the engine computer is not getting the "AC request" signal to operate the compressor and fans.....or it may be prohibiting AC operation for some reason.


Got a wiring diagram? Got test equipment?

Go to the compressor connector, there should be 3 wires in it. Compressor side of the connector has all red wires.
Ohm test on the 2 outer red wires, there should be continuity.
Yes? No?

jmille25

Thanks for the reply. I have access to wiring diagrams and test equipment. Tested the two outer wires...no continuity.

ezone

Thermal protector is open circuit.

I would temporarily bypass it with a jumper to make sure the rest of the system will work......then replace the thermal protector.

HTH

jmille25

Jumped the wires...both fans came on and the clutch engaged! Thank you very much for the help. Will get the parts ordered and everything buttoned up in the next few days.

ezone

YW. I believe the protector is held in place with a dab of RTV silicone.

pantdino

Well, for my car there was no continuity between the two outside red wires, but jumping the corresponding wires on the car side of the connector caused the fans to come on and the engine rpm to increase BUT the clutch still does not engage.

What is my next step?

Thank you again

Jim

ezone

The clutch cannot engage because it's unplugged. The center wire in that 3 wire connector is for the clutch. You would have to run one more wire between the center pin of each connector half to supply power to the clutch.
If you are testing on the compressor side connector, then it sounds like your thermal protector is open.


HTH

pantdino

Or run a jumper to the positive battery terminal?

I tested the two relays that show an A/C symbol and they are both good.

pantdino

On another topic- I got 75psi with my manifold gauge set (on both hi and low sides, with the compressor not running obviously). Is that about right?

Could the system be under- or over-charged in addition to the protector being out?

It looks like you have to remove the alternator to get to the top of the A/C compressor. Correct?

ezone

That would only show that the clutch works, or not.

It would not show if the AC system is able to supply power to it correctly. You could repeat the previous test with a voltmeter connected to the center terminal too, but the voltmeter can't put the same load on the circuit.

Depends on the temperature of the system. That's plenty enough pressure to get the system to engage and run though.
Sure.
You cannot determine this from just a static pressure reading though.

CLUE: A system can never become overcharged by itself just sitting around. It cannot gain more freon out of nowhere. It has to have human intervention to overcharge it.
Probably....Can you reach it with the PS and alternator in place?

pantdino

I ran a jumper from the pos battery terminal to the center position on the compressor side and jumped the outside pins on the car side. The clutch did not engage. But I was using like a 20 ga wire for the jumper, so maybe it wasn't enough amps to do the job.

If I use a larger jumper wire with the ignition on should I hear the clutch click to engage? The clutch is grounded on the compressor, I assume?

Where is the temperature protector on this car? I've googled and looked on youtube and can't find it.

ezone

The clutch is only about 3 amps, give or take.

You probably should measure the resistance of the clutch coil (guess: 3-4 ohms?) and calculate the actual amp load. If the resistance is high or open circuit, the coil is probably bad (barring some odd wiring fault).
Yes it's using chassis ground like most other components.


IF the clutch engages you should hear a loud click.

If no click:
If the coil is good (resistance check) and power is applied, there will be a magnetic field created. A long screwdriver should stick noticeably to the face of the pulley.

If the clearance is so excessive that the clutch plate can't pull in, you may push on the ring and see if it sticks to the pulley. Excess clearance might not be unusual at high mileage due to wear of the surfaces.


If you mean the thermal protector on the compressor, it's on the outside of the compressor. Follow its wires.

pantdino

"You probably should measure the resistance of the clutch coil (guess: 3-4 ohms?) "

I hate to admit my ignorance, but would I do that by measuring the resistance between the center contact in the connector to the compressor and ground?

ezone

That sounds correct.

You can use the neg terminal of the battery as ground, or the body of the compressor as ground, or whatever is most convenient and clean for good contact.

HTH

pantdino

summary:

no continuity between outside red wires on compressor side of connector

no continuity between center red wire and negative battery terminal

supplying 12v to center red wire to compressor with engine running, A/C switch on, and blower running --> no click from clutch or engagement

so both the clutch and thermal protector are bad?

ezone

Yes...but that sure sounds like an odd combination (both items bad at the same time)....Got mice?
Actually seen the wires on top of the compressor, look for damage?

The clutch coil usually has both a power and a ground wire, its ground wire is probably bolted to the top of the compressor.


Was your ohm meter set on the correct scale for the tests?? (BTDT)

You don't need to have the engine running, it should CLICK whenever power is applied, so you can play with it after the PS and alt are removed.

pantdino

The ohm meter was set to the 200 scale, which is the lowest it has. Meter never budged from 1, which is its display for infinity ohms. when I touch the probes together I get like 0.6 ohms, so I think it would have registered 3-4

It looks like if I pull the left front wheel I can see the top of the compressor thru the wheel well-- otherwise it's blocked by the alt.

This is the car that someone swapped an EX motor into, so I guess it's possible they forgot to connect a ground somewhere.

pantdino

with the outside 2 contacts on the car side of the connector jumped to each other, should I see 12v at the center contact?

That will tell me the computer is telling the clutch to engage, no?

Thank you for all your help

Jim

ezone

Yes, as a basic test...
but not only 12v, there must be sufficient amperage available on the circuit to run the clutch too. High resistance can cause hair pulling and make you doubt your sanity.

But I think the other 2 issues you already found are enough.
Yes, that sounds like the system is doing what it is supposed to doYW

pantdino

With the two outside contacts shunted to each other the fans come on but I do not get any voltage at the center contact to the compressor.

Next place to look for a problem?

Thank you

ezone

I spoke too soon huh?

Um....then I'd go to the clutch relay,
see if it clicks when you do the above.
Then check the fuse that runs the clutch (#1)
Then....
Then.....

I usually just pull the relay out to check what's going on with the 4 terminals underneath it. Test light (mine only draws about 50mA so it won't hurt electronics on this test) and/or voltmeter as necessary.

I can check this in about 10 seconds, if all is well I'd see my test light light up on 2 powers and 2 grounds. If your clutch is open then one of the 'grounds' at the relay socket would be missing.
So the relay is fed by 2 fuses supplying power to it.
The PCM controls ground to one side of the relay coil
The clutch is the remaining connection on the 'contacts' set of pins.

Here's a basic generic diagram



Where they have the jumper placed in the pic across 3 and 5, would engage the clutch on yours --if all was well.

So #3 and 5, one terminal has power from a fuse and the other terminal goes to the clutch.

#1 and 2, one has power from a different fuse, the other would be grounded whenever the PCM turns the relay on.

Biscuit

Is there wetness on either end of the body of the compressor? If so, there is a leak there.

pantdino

Update-- It seemed to me the coil on the compressor was defective so I set about replacing it, but I couldn't get the second snap ring off.


So I put it back together and had my son take it to a excellent AC shop. They said they got the clutch to engage and the system is fully charged and functioning so they set about finding the electrical problem.


They spent 2 days on it and couldn't find the problem so they had a specialist come in, who couldn't find the problem either. The specialist said he had this happen once and the dealer had to reprogram something to make the system work.


Does that make any sense? I know cars have a zillion microprocessors these days, but reprogramming an AC control module?


This is the car where someone put an EX motor in an LX. Could that be the issue?


My thought was to just run a switch to the dash to engage the compressor manually when you want it on. (Or even just to the grille area, since you usually know when you're going to need AC when you get in a car.)


Thanks again,


Jim

ezone

There are 3 main computers involved in 7th gen AC operation: The HVAC control unit in the center panel, the MICU in the fusebox, and the PCM.

If the system is inoperative, it's pretty easy to track a problem down, but it can be a real hair puller if there is more than a single problem. Might be a whole lot worse if someone hacked up the thing with the engine replacement.

What year is your car? Trans?
Which PCM does it have?
And which engine wiring harness, EX or LX?

What DOES work when you turn your AC on?

pantdino

from post #7 above:


Well, for my car there was no continuity between the two outside red wires (on the compressor side), but jumping the corresponding wires on the car side of the connector caused the fans to come on and the engine rpm to increase BUT the clutch still does not engage.


I don't know how the AC shop got the clutch to engage, since when I applied voltage to the center wire per your instructions earlier it didn't.


I'm really tempted to take the car back to them and just tell them to install a manual switch on the dash.


The engine has an EX harness, 2004, auto tranny.


My main question is, "Is there such a thing as reprogramming a module to fix this?" If the answer is "No, you just have to replace things until you find the problem" then I'm in favor of the manual switch plan.


Thanks again,


Jim

ezone

Been under the weather, feeling like I got hit by a truck....



No reprogramming or anything.
Your idea of manual switch is no good, this system must cycle on and off during operation. If you run the compressor all the time you'll freeze the evaporator or do other damage.



You have the thermal protector jumpered (bypassed) and the radiator fans now run when you turn the AC on at the dash controls?

Have you rechecked this?

Apply power to the compressor clutch, is there any spark indicating it's trying to flow electricity? If you push on the clutch with your hand, does it engage?

pantdino

I'm sorry you're feeling poorly -- hope you get well soon.


I discussed the need to cycle issue with my son, and he says he never leaves it on for very long because it costs gas mileage. Anyway he only uses that car for short trips. He and his wife take their other car for longer trips.


Unfortunately there is so little room above the compressor I can't even see the thermal protector or anything else.


Thanks for your help- I doubted there was anything like "programming" a controller.


Jim

ezone

Putting the compressor on a switch won't do any good yet anyway, you can't get it to engage.

Get the clutch to engage and the system may be OK again.

If it has a ton of miles, there may be wear and excessive gap, this can prevent engagement even while electrically appearing as it should. This is why I suggest apply power then push on the clutch plate to see if it engages.

pantdino

The AC shop said they did get the clutch to engage.


Maybe I'll have to have my son go back and have them label the wire they put power to that caused it to engage. When I put power to the center wire to the compressor with the side wires shorted on the car side of the connector it still didn't engage, but maybe I didn't do it right.