The "Help! My a/c quit!" post - Maintenance and Repair Forum

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The "Help! My a/c quit!" post
Thursday, July 17, 2003 4:24 PM
Since this becomes a recurring post during the summer months, I
thought I'd put together an FAQ type post to help explain just how an
air conditioning system works, what problems can arise with them, and
how they can be fixed.

Part I - The Air Conditioning System's Components

Most automotive air conditioning systems are made up of the same
components. By knowing what they are and how they work, you may be
able to save yourself a little time troubleshooting, or a few dollars
on a repair bill if you know what's going on ahead of time.

Freon: Freon is the refrigerant used in air conditioning systems. It's
purpose is to circulate through the system, transferring heat absorbed
by the evaporator (see below) and discharging that heat through the
condenser (see below).

For automotive usage, two types of freon have been used, designated
R-12 and R134a. R12 was the industry standard up until the years in
and between 1994 through 1996. Between these years, automakers were
told they had to switch from R-12 to R-134a, due to environmental
purposes. If your car is newer than 1996, it is 100% sure to be R134a.
If it is older than 1994, it is 99.9% sure to be R12. It is possible
to convert an R12 system to an R134a system, which will be discussed

Compressor: The compressor is the heart of the air conditioning
system. It's purpose is to pressurize and circulate the freon. The
compressor is made up of two parts: the compressor body and the
clutch/coil/hub/bearing assembly.

The compressor body is the non-servicible rear portion that actually
does the compressing.

The front portion, which the drive belt runs on, is multiple pieces
and can be serviced individually if desired. The clutch portion is
responsible for engaging the compressor on and off. Contrary to
popular belief, the a/c compressor is not working 100% of the time the
belt is spinning, only whenever this clutch is engaged. The coil is
the electrical portion which determines when the clutch will engage
and disengage. The hub is the portion which the belt runs on, and the
bearing allows the assembly to freely rotate.

Condenser: The condenser is the large coiled assembly located in front
of your vehicle's radiator. It's function is similar to that of a
radiator as well. It removes the heat from the refrigerant, changing
it from a hot vapor to a warm liquid.

Evaporator: The evaporator core is the non-visible part of your air
conditioning system. It is located inside your passenger compartment,
usually in close proxemity to your heater core, and removes the heat
and humidity from the passenger compartment.

Expansion Valve - or - Oriface Tube: The expansion valve or oriface tube's job is to regulate pressures throughout the system. An air conditioning system will have one or the other. If it has an oriface tube as opposed to an expansion valve, the oriface tube acts as an additional system filter as well.

Accumulator - or - Reciever Drier: The accumulator's job is to remove moisture from the air conditioning system, and to also allow any sediments or contaminents to settle out. This item is the circular canister that is visible in the engine compartment.

Part II - Troubleshooting the Air Conditioning System

Now comes the part you all are probably wanting, what to do, check and have replaced or repaired if your air conditioning system stops cooling properly.

Step One: The first step is to make sure the system is full of freon. There are one or two pressure switches built into the air conditioning lines that will not allow the compressor to operate if system pressures get too high (caused by obstruction) or too low (low freon amounts).

The first step in examining freon levels is to have SOMEONE that has a set of professional air conditioning pressure gauges examine the current system's pressure. This is why I usually do not recommend one of the "fill it yourself" kits available from most retail stores. The reason is, these kits only include one pressure gauge, and a proper air conditioning diagnosis cannot be done without examining both the suction and discharge sides' pressures.

Once the pressures are determined, if the system is low on freon, recharge it. If the system is the older (R12) style of freon, it is recommended to retrofit it to use R134a freon, as R12 freon is quite costly compared to R134a. The retrofit procedure is done by <b>completely</b> evacuating the system of R12, replacing the service port fittings, and recharging the system with R134a. The use of an evacuation/recharge-machine-safe UV dye is recommended.

Once the system is recharged, check the system for leaks. This can be done with either a freon "sniffer", or with a black light if a UV dye has been added to the system.

If all the system needed was a recharge, and no obvious leaks are detected, the system should be operable. A recharge every now and then is considered normal, as a small amout of freon does start to seep out with age, as the various seals, gaskets and o-rings throughout the system begin to get brittle and lose their sealing ability. If you are needing to recharge the system as frequently as every other year, there is a leak that needs to be repaired.

If you recharge the system and the pressures on both gauges read in their normal levels, yet the system is still not cooling, the first thing to check is for proper compressor operation.

Usually, the compressor clutch is operated by a relay. Test to make sure that the compressor clutch is getting the correct voltages at the correct times. If not, there is an electrical problem that will have to be tracked down. If the voltages are ok, check to see if the clutch is either burned up or locked up. If this is the case, the recommended procedure is to buy a new or remanufactured clutch, coil, hub and bearing assembly, as it is wise to replace these as a set, for prevention's sake.

NOTE: Before any system componants are replaced, the system must be fully discharged of any refrigerant.

If the clutch is switching on and off correctly and is physically able to operate, check to make sure the compressor itself is not locked. Usually if the a/c drive belt was thrown off, this has already happened. If this has happened, the compressor will need to be replaced. If a compressor replacement must be done, it is wise to replace the accumulator, and if applicable, the oriface tube, as these act as system filters, and will not allow system contaminants to reach the new compressor. A parts store or repair shop will usually not warranty a compressor unless there is proof that the accumulator and oriface have been changed also. Compressors are available with or without a clutch assembly; I personally recommend buying only those compressors with a new clutch, once again, for prevention's sake.

If there is any other componant leaking, it must be replaced, or if absolutely neccesary, repaired.

One last situation is that the system is full to capacity, the compressor clutch is operating as it should, and the compressor is functional, but either the suction or discharge side pressures are not correct. This is usually the sign of a blockage somewhere within the system. It is advisable to replace the oriface tube if equipped, or to first replace the expansion valve, if equipped. If these items have been replaced once, and either the oriface tube becomes plugged again, the expansion valve becomes inoperable again, or the gauges still show incorrect pressures, this is either a sign of a restriction within a line, the evaporater or condenser, or a sign of impending compressor failure.

In any case, if a restriction is found, it is recommended to flush the system entirely, replacing whichever componants are unable to be flushed, and recharging. If restrictions continue to occur, it is usually the compressor coming apart internally, and compressor replacement must occur.

For those of you that read through all that, congratulations. You now know the basic operations of an automotive air conditioning system. <br>

<br><br><br><br><br><img src=""><br><br><font face=Arial size=-3 >Ambassador - J Car Club of Indiana,
Fiero - Have you had your brush with death today?

Re: The "Help! My a/c quit!" post
Thursday, July 17, 2003 7:08 PM
I'd like to point out that in 3rd Gens, the compressor will be engaged at all times when A/C is requested, as they vary displacement based on load, and not vary their cycle.


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Re: The "Help! My a/c quit!" post
Thursday, July 17, 2003 8:45 PM
Bah! Stupid variable displacement compressors. <br>

<br><br><br><br><br><img src=""><br><br><font face=Arial size=-3 >Ambassador - J Car Club of Indiana,
Fiero - Have you had your brush with death today?
Re: The "Help! My a/c quit!" post
Sunday, July 20, 2003 5:05 AM
Z and BowTie -
Very informative thread. Thanks a lot, gentlemen! This will help many of us know what to ask/look for when we have to take our cars in for AC service. I know it'll help me, anyhow.
XLXRider <br>

"Paint - The Final Frontier"
Re: The "Help! My a/c quit!" post
Sunday, July 20, 2003 7:12 AM

Excellent information and presented well. I have two points for consideration:

1) It is my understanding that only licensed technicians are allowed to possess R12. Anyone else (general public) caught purchasing R12 can be subject to a serious fine, and the seller up to $10,000 in fines, loss of license, and jail time.

2) In addition to retrofitting a car to 134a, the accumulator/filter drier must be replaced as well. Any time an A/C system has been 'opened', which will be the case because the service ports are replaced after the system has been evacuated. Driers are cheap, so I liken replacing those to cheap insurance. <br>

"Beer is proof that God wants us to be happy" - Benjamin Franklin
Re: The "Help! My a/c quit!" post
Thursday, July 24, 2003 7:00 AM
Cavy-Blazer: Not only must the person possessing R12 be a professional technician, but they, or the facility they work for must be licensed by the EPA. <br>

<br><br><br><br><br><img src=""><br><br><font face=Arial size=-3 >Ambassador - J Car Club of Indiana,
Fiero - Have you had your brush with death today?
Re: The "Help! My a/c quit!" post
Saturday, August 02, 2003 3:05 PM
good info, and the posts regarding this are showing up again. Let's move it back up.


Sig removed because some people cry too much.<br>
</a>Scott Heflin, President Team Forward Motion <a href="" target="_blank">TFM </a> <a href="">Email</a>
Re: The "Help! My a/c quit!" post
Sunday, August 03, 2003 7:43 PM
Okay, so what is wrong with my A/C.... I hit the A/C button in my car but nothing happens. I don't hear any compressors come on or anything -- it is still straight warm air. <br>

"...It's guts and love and glory,
One mortal's chance at fame.
His legacy is rodeo
And cowboy is his name."
Re: The "Help! My a/c quit!" post
Monday, August 18, 2003 8:44 PM
Could anybody supply a picture as of where to use the A/C tanks?......I have a friend that can supply me with the Gauges, i just gotta make sure i know where to use the tank and sych.

All help and info is greatly appreciated ^_^


I love to smoke Civics!...........In reverse =D
Re: The
Tuesday, August 19, 2003 7:16 AM
Zline don't forget that R-12 is Freon and R-134a is SUVA


Re: The
Tuesday, August 19, 2003 6:36 PM
First off Good read learned a little. OK i have narrowed it down to the oriface tube but my question is where is it i have a 97 Z and i can not find my haynes manual any help would be great thanks David

Re: The
Thursday, August 21, 2003 9:52 AM
I have the same problem... nothing kicks on. I tried to recharge it but it won't even turn on. So, from your reading, I would think to check the relay first? Do i buy a new one, or is there a way to temporarly bypass it? If that is not the problem, I will not spend the money to fix it, since it seems like it could get high. Let me know guys. thanks.
Re: The
Thursday, August 21, 2003 8:11 PM
Low refrigerant is the majority of no cooling on gm cars. This is the quick and easy way to check it. Open your hood. Crank your car. Turn on your a/c, turn fan to highest setting. Look at clutch on A/C compressor and see if the head is spinning. If the center is not spinning, try this. Find the accumulator, it is the silver canister on the left hand side of the engine compartment with hoses tied to it. There is a little plastic thing sticking out of the side of it. This little jewel is known as the low pressure cut off switch or LPCO. This small switch is a pressure switch and when the refrigerant level gets too low, it kills the clutch drive on the compressor. Why? because the refrigerant acts as a coolant for the compressor along with the oil. IF there is a leak or blockage, little or less freon is being fed to the compressor. If the switch didn't cut off the compressor, the compressor will overheat, expand, and lock up. Same as if you run your engine with no oil or no antifreeze/water. Friction and heat will fuse it locked. Back to the switch. Undo the wiring harness to it, usually a little plastic clip. If unplugged the canister will have two prongs sticking out of it. Now, the wiring harness still in hand, take a piece of wire (14 gauge or pretty thick) cut the wire about 10 inches long and strip the coating off the wire on both ends about an inch. Take the wire and insert it into the wiring harness, one end on one side where the prong went in and one on the other side of the wire where the prongs went in. IF the compressor clutch engages it means you have low refrigerant pressure, a.k.a. low charge. This should be done only for a short time, do not jump it out and leave it this way. Or like said above, you'll burnout the compressor. You have narrowed it down to low charge, a restriction in the line somewhere (like putting your finger on the end of a garden hose, water coming through but not enough to maintain proper pressure) or a bad low pressure cut off switch. This is the majority of the problem and the best starting point. If the compressor isn't running nothing else matters. Do this little check and it will save you alot of trouble. You can do this as well to help pull a vacuum to charge the system. Not the best way to do it, but when your on a budget like most, it's all you got. I hope this helps people save alot of time (AND hopefully alot of money). Just remember, think simple. Getting power, not electrical.
Re: The
Saturday, August 23, 2003 7:21 AM
I've read and read and read, searched and searched and searched.

I still can't figure out where to use the tanks?.....Where do i plug the charging tanks into?....
My Boss told me its that metal tube that runs along the inside of the passengerside fender, with the blue plug?......But i dunno, he drives fords, Lol

If anyone could give a good description, Or supply a picture,....I'd appreciate it.


I love to smoke Civics!...........In reverse =D
Re: The
Friday, August 29, 2003 6:37 AM
thats it...the blue cap one.
Re: The
Saturday, August 30, 2003 6:39 PM
i need some help. my engine is overheating and my A/C keeps turning on and off when i switch it on.
Re: The
Sunday, March 07, 2004 11:34 AM
FOX, must be 98 and up the pressure switch is not located in the acumlator, i think the switch is actuall a half inch from the high pressure port and has 3 wires not 2

Its not how fast your car goes....its how much nerve the driver has to push it that fast.
Re: The
Monday, March 08, 2004 6:56 AM
a/c....who needs that???

even when it did work i still always had the windows down <br>

Re: The
Thursday, March 11, 2004 7:03 AM
Well, add me to the list where the AC does not work, but sometimes when I turn the AC on, the compressor will turn on and off very quickly, but will not engage all the way.

any ideas?

Re: The
Thursday, March 11, 2004 12:32 PM
cheba wrote:Well, add me to the list where the AC does not work, but sometimes when I turn the AC on, the compressor will turn on and off very quickly, but will not engage all the way.

any ideas?

Sounds like the system is low on freon, and will not allow the compressor to engage for it's own safety; have the freon level tested.
Re: The
Monday, March 15, 2004 10:02 PM
I had a different engine put in and when I turned on my A/C it felt as if it wasn't blowing cold air... Took the car back to my mechanic he reached down and twisted some kind of knob on the compressor and it started to blow cold air... few months went by and now im at square one. Does anyone know if there is a freon adjustment screw or something along those lines on the compressor?

thanks, <br>

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<img src= "">

Re: A/C problem 99 Z24
Sunday, March 21, 2004 7:00 PM
I have a 1999 Z24 with 95 thousand miles. When I push the A/C button, the light comes on but it is now rare that I hear the compressor engage (and when it does engage it shuts off on its own moments later). I checked the fuses (swopped the one under the hood with the fuel pump) - everything is ok. Is there another electronic component that I should check? Could my system just be low on freon? Are there any other Z24 owners who have had a similar problem and if so, what did you do to correct the problem? Please help.
Re: A/C problem 99 Z24
Wednesday, April 21, 2004 8:51 AM
My pump will not come on. I put the gauge on the sytsem and it was overcharged. So I let out some stuff but the clutch still will not engage.

My question which plug turns on the pum so I can jump the prongs. Is it the 2 wire plug down by the AC pulley or the 3 wire plug on top of the AC Compressor?
so can i service my compressor?
Thursday, April 22, 2004 11:25 AM
I had my a/c checked and they said it is leaking behind the compressor pulley...if I read the forst post correctly this part should be user servicable, or do I still have to buy a new compressor?
Re: so can i service my compressor?
Monday, April 26, 2004 2:25 PM
It is possible to replace just the shaft seal, however, this still isn't something I'd recommend for a do-it-yourselfer. <br>

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