My AC is blowing cool - but not cold, and with temps in t he 90's all week, cool won't cut it. Anyway, my system is full of fridgerant, the compressor functions, and the ac clutch engages when AC is turned on. I noticed in the fuse box under the hood, there was a diode labed "AC diode". What does this do? I took it out, and it doesn't seem to make any difference in the operation of the system.





Any help or suggestions would be greatly appriciated.





Thanks!

 

The a/c diode is for shunting the voltage created from the clutch coil when the a/c is turned off, preventing the a/c relay contacts from arcing as the contacts separate. Its technically described as inductive reaction when the clutch coil's magnetic field collapses. As you've noticed, there's isn't any change in the way the a/c operates because this diode works silently on the electrical circuit neither to improve cooling nor detract from it. Its purely for electrical stability. Leave it plugged in.


Unless you are trained in a/c systems and understand the utility of a/c hi/lo pressure gauges you're guessing from stating the a/c is "full of fridgerant, the compressor functions, and the ac clutch engages when AC is turned on". The fact that your seat-of-the-pants feeling of less cooling is good enough w/o using the store bought gauge. One of the few methods for determining a/c refrigerant capacity is to measure the low pressure side but not, as I suspect the way you did, at idle as no one drives at idle speed. Measuring the low pressure is done at engine speeds from 1500-2000 rpm as specified in the factory/field manuals, somewhere closer to the speeds everyone drives in real world terms. Those store bought canisters seldom instruct anyone to raise their idling rpm's to 2000 for fear of liability suggesting this for a parked vehicle. A/C work is done at up to 2000 rpm with all the safety common sense dictates. The pressure is monitored and if necessary, barring any major repairs or leaks found, refrigerant is injected to a specific pressure relative to ambient temperature and humidity. The carinterior's center vent is also temperature monitored with the fan on med-high to correlate gauge pressures with vent temperatures. Not a casual charge and go routine for anyone seriously desiring to understand a/c work but what goes on in any a/c repair shop.


Your system is probably low on refrigerant and needs, at the minimum, a visual inspectionfor any signs of a leak. A temperature probe (dial type $5) inserted into the center vent with the fan on medium and charging the system into the low side service valve, stopping a bit to monitor the pressure so overfilling doesn't occur will probably work for some. Overfilling with refrigerant is just as bad as a low amount because excess refrigerant overloads the compressor, causes higher pressures that can lead to overheating of the compressor damaging it permanently, burst hoses, blowing fuses, and loading the engine down. Only the right amount of replacement refrigerant should be injected; as per specified engine rpm, pressure, interior car temperature, and outside temperature/humidity conditions. In other words, a little more than charge and go. Not difficult to do but if done incorrectly may lead to expensive repairs otherwise leave it for a pro.

 

Thanks for the reply. After sending my original post, it dawned on me that "AC" probably stands for aletrnating current and not air conditioning. In spite of that blunder, I am not as dense as you might think.





I DID measure the refigerant pressure with the appropriate gaging, rather than "flying by the seat of my pants". I also had my lovelyassistant hold the RPM's around 2000 as well. As far as measuring the temperature of the air coming out of the center vent, I didn't use one of those new fangled dial type temperature probes as you suggested, rather I opted for a Dataq DI-730 data acquisition system equipped with a DI75B signal conditioning backpack to more accurately correlate the system pressure measured with Sensotec TJE pressure transducers to the ambient andAC system temperatures - I have been an instrumentation specialist in my company's metrology lab for almost 10 years now, so I have access to all sorts of cool "toys".

 

Wow! All them cool toys to find out your low on refrigerant! If you have the time you may be interested in the temperature/pressure chart for R134a to correlate further anomalies. Any good digital temperature probe will do just as well as over the top data acquisition tools but I must admit I'm a bit envious of you having a lovely assistant. I apologize if I came across treating you as dense ascontrary to your opinion these message boards aren'tfilled with many cerebrals willing to understand the nuances of air conditioning and the dangers associated with it. I'm not going to explain the shortcuts of a/c as Iwill not accept any blame for the blunders of others if I spell it out in its entirety what takes place during a simple a/c pressure check but to elaborate the unforeseen consequences of individual actionsperforming something I feel requires as much explanation aspossible in hopes of making the individual aware of the risks. If I have created some doubt as to the safety aspects of a/c work then I may have turned someone away from home DIY repairs to seek professional help. Perhaps this isn't what he/she expected and I'm comfortable with that. Calculated risk taking on my part by sharing essential information to be aware of. I'm sure you can understand what 250 psi of liquid refrigerant will do toa person unfamiliar with a/c presurescaught in the midst of a/c repairs while running at above idle rpm's if a hose burst. As far as I'm concerned its safety first then attempting repairs second. This is a public message board and I prefer to convey as much information as possible to the point of being long winded.

 

Ducky -


No worries.......I tend to get easily annoyed when people use superfluous words when diminutive ones would suffice ; ) I appreciate any knowledge that people are inclined to share with me.





Since I have pretty much ruled out the low refrigerant possiblity, I am going to take a closer look at the condenser, receiver/drier and evaporator. I am hoping it will be something as simple as cleaning up the condenser.





On the up side, since the air isn't working in the Saturn, it gave me an excuse to ride the Harley to work today!





By the way, my lovely assistant is actually my husband and he's really more burly than he is lovely - I just call him that to get on his nerves.





Bridgett

 

Ha ha ha, L O L !Perhaps you and I can rendezvous for a secret meeting................ to repair your 'uncool' car of course! That's just like you women, wrapping us around your finger!? I was called a pet name by a former girfriend that ordinarily would inflame most men about our male attributes but I took it in stride because we were then very intimate and close.


There are several things to check; the radiator/condenser fan running when the a/c is on, blockage of the coils from road trash like newspapers, plastic bags, etc., the evaporator/heater door actuator stuck in position allowing heat to mix with the cool air, overcharging of R134a (or R12), and last, a low amount of refrigerant. If you can post the system pressures at whatever outside temps are, engine rpm, and in-dash temps, we can figure out what's lacking. If not, try http://ackits.comand ask the experts there for advice as they have an answer board and online retail sales for everything a/c. I have no affiliation with them but find their information base a good source ofreference. BTW, if it helps any (assuming a R134a system), at 80 d F., 2k rpm, low pressure should be around25 psi or no lower than 40d F.dash temperature while the high side can range up to 220 psi.Both pressures can vary due to humidity and airflow through the condenser/radiator area.