New here, looking for some knowledgeable advice on an issue with my car's AC

[flyawayfromfate]

Hey there,

I don't know if this is the correct place to post this, so I'm sorry if it is misplaced. I was searching for forums with people who would have some knowledge about my car and weed out responses from people just taking a guess.

I bought my 2003 Toyota Matrix XRS used this past March from a licensed resale dealer with signed contracts, warrantes, repair reports, the whole nine yards...in other words I didn't purchase my vehicle from someone selling on craigslist with no knowledge of the condition of the car. When I was testing it out I included testing the ac and heating and found them to both be working well. It was spring at the time and the AC blew cold air and I was satisfied.

Once it started getting hotter outside and I used the AC more often, I noticed that the hotter it got outside made it harder for the AC to keep the air cool. After a couple of months I then noticed that it would get luque warm then blow cooler every so often. Few more months later it's progressed to cooling the air less and less until it completely cut out during a drive a month ago.

I tested the compressor by idling with it on the coldest setting at fullblast with the AC button on. It turned on and off with me switching the AC on and off, so I figured the compressor was working correctly. I then thought that maybe the freon needed to be recharged and bought a can that came with a pressure gauge, which measured it being a little low.

Since I bought it used with only one previous owner I figured that the freon in the line hadn't been touched since the car was made. I emptied out most of the freon with the AC running on low and then followed the instructions on the can to replace the lube and charged it until the pressure levels read correctly. After I did this the air in my car blew extremely cold but on the drive back to my house it slowly got warmer until it was blowing hot again. When I got home I checked the pressures again and it then measured a little high. I released some pressure from the lines, waited and checked that it was then at the correct pressure. The next few times I drove it, it acted the same way it did before it was charged except it now blows extremely cold air when it does turn on.

The compressor still turns on and off when I switch the AC on and off. This past month after it was charged the times it's blowing cooled air I paid attention to how cold it was and it hasn't gotten weaker. This makes me think that it isn't a leak because I would expect it to slowly get weaker like it had previously. I have also noticed that if it starts blowing cold while the car is idling it sounds stressed as if it were trying to die but it hasn't effected how the car drives when I'm giving it gas. I've also noticed a strange smell when it is blowing cooled air, but I suspect this is only because it was just charged. I'm mentioning it though because I'm not sure.

In asking in forums I've had a few people mention that it might be a control switch, and in searching I believe they mean either this switch:
http://www.autozone.com/autozone/par..._311128_16190_

or this switch:
http://www.autozone.com/autozone/par...5_304641_3718_

I'm 21 and Female so unfortunately after taking it to 3 different mechanics I've gotten 3 completely different answers, all of which are really expensive. I don't want to be taken advantage of, and given that it does still put out cooled air tells me that it is probably a small electrical/sensor part that has gone bad.

Thanks for any help or advice I get from you guys, and hopefully I can get this done with inexpensively.

[TexasToyota]

From your description, it sounds like the compressor may be failing to engage when cooling is absent. You need to confirm this by observing whether the compressor clutch pate (front center section of compressor) is closing and turning. If it's not turning, the clutch plate is not engaging.

If it's not engaging, the likely reason is excess clutch plate gap. When gap gets too large, the clutch coil magnetic field won't close the clutch plate when coil is energized. You can measure the clutch gap w/ a feeler gauge. It should be about 20 mils +/- 5 mils. A mil is 1/1000 of inch.

Fix is to remove the clutch plate (1 bolt 6mm on most compressors), remove the clutch plate, and remove thinnest shim that get's gap to spec. Usually two shims beneath clutch plate.

It's also possible you have a faulty ac thermostat, pressure switch, or other intermittent electrical problem, but clutch gap is a frequent fault.

The only way to measure pressures correctly is w/ a manifold gauge set. You can buy an inexpensive set from Harbor Freight. Check AC systems videos on youtube by ericthecarguy, richpin06a, briansmoble1, and scottykilmer. These will provide basics of using ac manifold set.

You're doing better than about 95% of shade tree mechanics on AC systems. Keep up the good work.

good luck

[Ericss81]

I had the same problem. There is NOTHING wrong with your car! Charging your AC is NOT DIY maintenance, although you can buy recharging cans everywhere. They are only good if you need a little freon. The can only charges the one line, the larger pipe, of the AC and the other one stays low on pressure. If your system is low on freon you must take to a shop to be recharged. What they do is empty the system, wait 15 min or so to dry the moisture inside and than charge both "pipes" with the proper pressure. And you have AC again! I cost me 2 cans $30 each before I took it to a small local shop. 45 min and $75 later my AC was like new! The guy in the shop was nice enough to explain to me what I just wrote

[TexasToyota]

Your advice is sound but your understanding of AC system is not.

AC system is a continuous loop w/ high and low side connected. When you shut down AC, pressures equalize. When charge is low, the compressor is starved for refrigerant and low side is very low, and high side is low also, but much higher than low side, say 10 psi low and 125 psi high.

Only the expansion valve (small variable orifice) allows fluid to rapidly expand and create cooling in the evaporator. Compressor raises pressure to allow pressure drop across expansion valve.

good luck

[Ericss81]

Originally Posted by TexasToyota

Your advice is sound but your understanding of AC system is not.

AC system is a continuous loop w/ high and low side connected. When you shut down AC, pressures equalize. When charge is low, the compressor is starved for refrigerant and low side is very low, and high side is low also, but much higher than low side, say 10 psi low and 125 psi high.

Only the expansion valve (small variable orifice) allows fluid to rapidly expand and create cooling in the evaporator. Compressor raises pressure to allow pressure drop across expansion valve.

good luck

U r right I tried to explained smthg I understood when it was explained to me, like u did too, but I dont quite understand it. Sorry. Just wanted to share my experience and hopefully help the new trix sister Thank for the explanation. I'll try to remember it.