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I finally got my A/C working thanks to this forum and its awesome users. My only qualm is, a lot of the information is scattered, and it took a lot of time to find everything I needed to check out to get there. I've decided to compile an all-inclusive how-to on pin-pointing what's wrong, and hopefully save you some time.

For the record, everything pertains to a B5.5 1.8T. Steps are ordered from least-intensive to most-intensive, from "have a look" to "get your star keys out". I think this might be a little better than going back and forth under and over everything. Plus, as you go, you can check everything so that you can prevent further problems.

First, decide what your problem is. This could be no cold air, intermittent cold air, air that isn't cold enough, or other things.


What to check in the interior



  • Temperature Flap Servo (thanks to ScottPassat2.8)
The first thing you'll want to check is whether your temperature selector switch actually does anything. The way to do this is to get down in your front passenger footwell, look up and toward your stereo. Get a flashlight and look for this red arm bar:



Turn your car on as well as the A/C. Move your temperature selector from hot to cold while watching this red servo arm. It should go toward you for cold air, away from you for hot. If it doesn't, it's likely seized or dead. ScottPassat recommended tapping it.


  • A/C Clutch Relay (via skismatik)
While you're in there, check for this common problem.

Take off the fuse box cover and look inside. You should see a box that says "384". This is your A/C clutch relay.


First off, make sure that it's in the right place. Now, take it out. If you have small hands like me, it's not a big deal, but if you have trouble maneuvering into there, try using pliers or take off that part of the dashboard.

Get a screwdriver and on the bottom where the pins are, jimmy the plastic cover off. You'll see this:



Flip it over and look here.


If that red circled joint looks cracked, touch it up with a soldering iron. Then, put it back together and put it back in. Unless the relay is dead, this should work.

What to check under the hood:


  • Refrigerant Level
Pop your hood open. Take the plastic cover off the area where the battery and cabin air filter is:


Unscrew the black cover from the yellow circled hose.

Grab a refrigerant gauge. You can find these bundled with refill refrigerant cans. Turn your car on, set the A/C temp to coldest full blast, and let it run for about five minutes.

Measure the refrigerant level. The pressure depends on the ambient temperature. This should be explained on your can of refrigerant, but if it isn't here's a guideline:

65F/18C: 25-35psi, 172-241kPa
70F/21C: 35-40psi, 241-276kPa
75F/24C: 35-45psi, 241-310kPa
80F/27C: 40-50psi, 276-345kPa
85F/29C: 45-55psi, 310-379kPa
90F/32C: 45-55psi, 310-379kPa
95F/35C: 50-55psi, 345-379kPa
100F/38C: 50-55psi, 345-379kPa
105F/41C: 50-55psi, 345-379kPa
110F/43C: 50-55psi, 345-379kPa

If your refrigerant pressure is outside this range, either put some more in, or let some out (wrap a screwdriver in a towel, push on the valve)

  • A/C Compressor (via V6er, others)
Lift the front of your car a little on jacks. Remove the belly pan. Climb under and look up at the engine. You'll see a bunch of pulleys. The one closest to the passenger-side headlamp is the one you'll need to be looking at.

Have someone turn the car on, and then turn the A/C on while you watch. The middle of this pulley should pop out and start spinning after they switch the A/C on.


(on the left)

That's your A/C clutch engaging. If the center doesn't start spinning, then your clutch isn't engaging. There are a number of reasons for this. In my case, there was a bright green wire just above the compressor that was disconnected. Or, the compressor might be dead or seized. Climb into your car, take off the fusebox, and put your hand on relay 384. Turn on the A/C-- you should feel the relay click.




So there's my troubleshooting guide. If anyone's got something to add, by all means. I did my best to make it easy-to-follow. Thanks again to everyone listed (and everyone else!) for keeping me cool on a burning Texas summer!
 

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Secondary Electric Fan

The secondary electric radiator fan should kick on when the AC compressor is running (passenger side of radiator). If it is not, you've got a problem. Inadequate airflow over the condenser coil will cause head pressure be high and in turn suction pressure will also be off. In this condition, gauge readings won't allow you to properly check the state of charge. The system will not produce consistent cold air. You may get cold air while moving at highway speeds but not when in slower traffic or while stopped.

Check for power to the fan (with AC compressor running). If no power, check the fuse protecting that circuit and the relays powering the fan. I believe the fuse is a 40Amp located under one of the the relay panels under the dash. Two relays control fan speed (one high and one low). They are located in the auxiliary relay panel (I think positions 5 & 8).

I've seen posts about a fan speed control module. I'm guessing that's something on models newer than mine (1999). This module would also be part of the aux fan circuit.

If the fan motor is getting power and ground but not spinning up, the fan motor itself is probably bad. Try spinning the fan by hand. If it does not spin freely, it's bad. If it spins up and runs only if you give it a push start with your hand, the fan motor is bad.
 

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Nice straightforward write up.
Simple to follow and should be of help to others.
Must be about time we had all this AC stuff in one place.
Would be nice to have just an AC section. I have asked before but nothing came of it.
 

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Great write up. Does anyone know how to diagnose a V6 climatroinic AC problem? My buddies won't blow cold air. I suspect the AC clutch but am not sure how to check it and what else to check.
 

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Great write up. Does anyone know how to diagnose a V6 climatroinic AC problem? My buddies won't blow cold air. I suspect the AC clutch but am not sure how to check it and what else to check.
I would start a new post,then go from there.
 

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100 psi.

The secondary electric radiator fan should kick on when the AC compressor is running (passenger side of radiator). If it is not, you've got a problem. Inadequate airflow over the condenser coil will cause head pressure be high and in turn suction pressure will also be off. In this condition, gauge readings won't allow you to properly check the state of charge. The system will not produce consistent cold air. You may get cold air while moving at highway speeds but not when in slower traffic or while stopped........
Attaching the guage to my 2005 5.5 I get a reading of right around 100psi while the A/C is NOT working. I did not know enough to check if the fan was running at that time.
But how could it possibly be this high, when the A/C system has never been touched since new and normal pressure should be no more than 38psi.
My problem is intermittent and the thing appears to be shutting down more as the ambient temp goes up. The fan makes sense here but when I check it right now it works, but so does the A/C right now.

Next I'll do a pressure reading while the system is working and will check if the fan is NOT working when the A/C is NOT working. I had the relay out and open and all appears to be normal in there.

Is it possible for the system to go to 100psi because the fan is not working??:banghead:

UPDATE: Took the car to Canadian Tire in Pickering and was told the entire AC system would be checked for $39.95. I was to get a report and firm quote. When I picked up the car they charged me $45 (inluding tax) and simply said they couldn't do the testing because my system had unidentifyable freon mixed in. This was obviously NOT TRUE since the system had never been touched by anyone and therefore had nothing but factory freon in it. $45 wasted. Even the Better Business Bureau was not able to get my $45 back from Canadian Tire. Took it to a small shop nearby and paid for an hours time to have the entire system checked. By process of elimination it was decided that it must be the relay even though it appeared to be ok. They put in a new relay the next day and one year later the AC is still working great without fail.
 

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Pressure will be higher if the compressor is not running. You are metering on the low pressure side, and when the compressor is not running, the pressure in the system equalizes, so the additional pressure from the high side will show in the low side.
 

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100 psi is the static vapor pressure of r134a at roughly 87ºF.



Your pressure is that high because your AC system is a closed system containing a "charge" of r134a. The ambiant air temps were probably about 87ºF when you did your measurement.

In order to check the amount of charge you need to have the system running (compressor, cabin blower motor and aux electric radiator fan).
 

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There is also a pressure switch that makes sure the refrigerant is in the acceptable range before allowing the compressor to kick in. This is mounted behind the bumper under the passenger turn signal/headlamp area. The connector on mine got pulled partially out during a timing belt job when I pulled the front end into service position, and caused total loss of A/C. If the pressure switch is not giving the proper signal, you will also not hear the electric fan kick in.
 

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R134a or 12a?

100 psi is the static vapor pressure of r134a at roughly 87ºF.

Your pressure is that high because your AC system is a closed system containing a "charge" of r134a. The ambiant air temps were probably about 87ºF when you did your measurement.

In order to check the amount of charge you need to have the system running (compressor, cabin blower motor and aux electric radiator fan).
Thanks for the quick replies!!!!!
Sure enough ambient was right around that 87F mark.
R134a is not available/illegal to be sold in Canada. PartSource sells the Red Tek 12a as an substitute and i get conflicting reports as to wether it can be safely mixed to top up my 134a system.
Any advice?

Just called the maker of RED TEK 12a and was told repeatedly that the 12a is "completely compatible with 134a". When asked if I could mix 12a into 134a for topping off the system I was told: "134a and RED TEK 12a are completely compatible". Sounds like they're not allowed to say "Yes you can mix them" -probably because of regulations regarding topping up refrigerants. I'll take it as a yes.
 

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Update

Today it's 90F or 32C here in Toronto and that automatically means my A/C won't work at all.
It allowed me to check the A/C fan and it is working well. The relay and clutch are not coming on today but all was working well last night after the ambient temp had dropped.

The hot/cold dial is working as it turns the hot air on when turned clockwise.

Question:
If the R134a is low would that prevent the relay to fire or would the relay turn the A/C on only to then have the sensor turn it off again after a short delay because of low freon?
But if a low state prevents the A/C from coming on then how would I add freon to the system? My understanding is that the thing has to run in order to add refrigerant.
Any help will be much appreciated.
 

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R134a is not available/illegal to be sold in Canada. PartSource sells the Red Tek 12a as an substitute and i get conflicting reports as to wether it can be safely mixed to top up my 134a system.
Any advice?
I don't know what Red-Tek-12a is, but it must not be R134a if local laws forbid its sale. Search around for an AC charging sale. You may need to farm this job out to someone licensed to handle the proper refrigerant.

Why you should stay away from Duracool/Red Tek/ R-12a - The Acura Legend & Acura RL Forum
 

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How can we recharge the 134a without the clutch engaging? Don't we need to have the AC running when adding refrigerant??:confused:

You can base pressurize the system from the charging bottle. That will be enough to engage the clutch. If your system is that low, you likely have a leak and the charge will not last long. If the system is empty, it really should be repaired, then pumped down to clear moisture and then filled.
 

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A/C pressure switch 129

You can base pressurize the system from the charging bottle. That will be enough to engage the clutch. If your system is that low, you likely have a leak and the charge will not last long. If the system is empty, it really should be repaired, then pumped down to clear moisture and then filled.
Thanks that explains it. I don't think the system is that low, if low at all.

The A/C is ice cold when the clutch engages and it engages when ambient temp is below say 70f. I would expect that if the refridgerant was low then the A/C would not blow as cold when it works.

I'm learning that the a/c pressure switch 129 would typically be the culprit when the clutch doesn't engage, especially on a diesel, which mine is.
Haven't had time yet to look but does anyone know the best way to get at that pressure switch?

Got to the pressure switch by removing grill and nose. Bridged term. 1 and 2 on the switch and still can't get the Compressor clutch to come on.
 

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There is also a pressure switch that makes sure the refrigerant is in the acceptable range before allowing the compressor to kick in. This is mounted behind the bumper under the passenger turn signal/headlamp area. The connector on mine got pulled partially out during a timing belt job when I pulled the front end into service position, and caused total loss of A/C. If the pressure switch is not giving the proper signal, you will also not hear the electric fan kick in.
I would take extra special care to make sure this connector is installed, particularly if you have had a timing belt job sometime before the warm seasons where you wouldn't have noticed a loss of A/C (it's about that time for all you B5'ers anyway). If you do not know, it is a fairly invasive process that involves disassembling most of the components on the nose of the car. I went out and bought a gauge to make sure my refigerant pressure was acceptable (my low pressure line rested at 65 PSI @ 55F with the system running full blast "A/C"), and the relay, fan, everything, seemed to check out. If you know your system to be reliable before a service, it's easy to be caught off guard by things someone else may have changed. In my case, the compressor was not allowed to run (as a fail-safe) because the technician failed to reconnect the pressure switch, and the system had no sensor data (this fault wont register with a VAGCOM scan).

Long story short, after getting frustrated with all my failed troubleshooting, I got on my knees, looked into the passenger side fog grille, and immediately saw the T4 harness for the pressure switch just dangling inside the grate, plain as day. Luckily, this is a fairly simple fix; just pop out the grille, grab it and reach up to the right where the sensor is mounted to the thick silver vertically-oriented A/C line (if you have larger hands it may take some coercion). It plugs straight downward.

IMG_20120414_150039.jpg

Instantly the familiar churning sound of the compressor came back and I was back in business.
 
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