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Toyota Corolla Moisture(?)

peanutaxis on Sat November 07, 2015 7:38 PM User is offline

Year: 1995
Make: Toyota
Model: Corolla
Engine Size: 1600
Refrigerant Type: R134a



Hi,

This 20YO car has never had an AC gas top up or service. Last summer my air con would blow vaguely cold for a minute and then blow warm. I figured it was low on gas so this summer I topped it up with 134a. Most of a can went in and it has held that pressure for a few weeks now. Problem is that it will blow cold for a few minutes and then blow warm. Somewhere I read that there can be moisture in the system which freezes in the expansion....valve is it called? I suspect this is what's happening.

So I was going to try to replace the receiver dryer. My question is, do I really need to go to the prohibitive expense of buying or paying someone to vacuum out the system to boil the moisture off? Surely most of the moisture will come out with the gas when I empty the system, and the tiny amount of moisture that is in the air that will then fill the lines would more than easily be absorbed by [a small fraction] of the dessicant in the new receiver dryer, wouldn't it?

thanks,
p


Cussboy on Sat November 07, 2015 8:38 PM User is offline

1. First thing I'd do would be to see if compressor clutch has disengaged when it starts to blow warm. If not, both high and low pressure readings at about 1500 rpm would be useful.


Quote
Originally posted by: peanutaxis
I figured it was low on gas so this summer I topped it up with 134a.


This is NOT a recommended practice, you were shooting in the dark unless you have lots more data that you didn't post.

No, do not replace the drier; if you have refrigerant in there, moisture doesn't get in. If you do replace that, you'd legally need to have the existing refrigerant recovered, and for any performance at all you'd have to have the system vacuumed for at least 30 minutes to remove moisture and air, if you want any decent AC performance.

To me, sounds like you should take it to an AC specialist, would be better and cheaper in the long run.

peanutaxis on Sun November 08, 2015 9:02 PM User is offline

Thanks Cussboy,

So it turns out that the compressor is staying on. All the time! I can turn the compressor off by the AC button or by turning the fan to zero, so no relay or mechanical-compressor problems to my understanding. I just went for a drive and kept the AC from stopping (expander freezing?) by switching the ac off and on every 10 seconds or so. That worked fine.

The only gauge I have is for the low end. When I let the system rest - AC off engine off for a good half hour - the gauge reads about 80-90psi. When I turn the AC on the gauge goes basically to zero, of course, because the compressor is constantly on.

Sensor problem?


thanks,
p

Cussboy on Sun November 08, 2015 10:31 PM User is offline

Does yours have a fan clutch or electric fans?

You need both high and low side gauges if you try to diagnose and fix yourself. Low pressure when operating should be like 30-40 psi at 1500 rpm, and high side should be like 200 to 250 psi. That 90 psi static pressure doesn't really tell much.

peanutaxis on Mon November 09, 2015 12:20 AM User is offline

Hi,

Electric fans. Low pressure side at idle is 0psi due to compressor being on constantly.

Edit: If I yank out the connector for the high pressure sensor, the compressor turns off. I can't find a low pressure sensor (it is an old car, after all. Maybe there isn't one).

Hi side should be fine as a lot of gas went in, and also because I have the same problem now that I had before I recharged: cool for a few minutes, then warm. The only thing that has changed is that it's cooler for those few minutes.

Edited: Mon November 09, 2015 at 2:39 AM by peanutaxis

Cussboy on Mon November 09, 2015 8:25 AM User is offline

high and low side pressures

peanutaxis on Tue November 10, 2015 8:46 PM User is offline

Quote
Originally posted by: Cussboy
high and low side pressures

I'll bet you can't even come up with a scenario where you need the Hi pressure side. You don't, because a too high or low Hi side pressure wouldn't explain things:

If the Hi side pressure is too low, then why does it blow so cold? And why would it blow really cold for several minutes and then go warm? If it's too high, then why would the the low pressure side always be virtually zero pressure whether it's blowing cold or hot? And why wouldn't the compressor do a safety-turn-off if the Hi side is too high? If it is blowing warm after 5 minutes because the expansion valve is closing fully, then why does the low pressure side read zero both when it's blowing cold and when it blows hot?


Even just the fact that the low side is zero while it's blowing really cold is enough to start. Why is it not cycling at 30-40psi? Is there a low side pressure switch somewhere (I can't find one) that's faulty. Or a temperature sensor somewhere......?






Edited: Tue November 10, 2015 at 8:50 PM by peanutaxis

Cussboy on Wed November 11, 2015 8:23 AM User is offline

Quote
Originally posted by: peanutaxis

I'll bet you can't even come up with a scenario where you need the Hi pressure side. You don't, because a too high or low Hi side pressure wouldn't explain things


I was asking if the high pressure reading remained the same when the vehicle went into the non-cool mode. How can I KNOW that you KNOW that the compressor is engaged, or engaged properly, I don't know your background with this.

So go ahead and try to justify to yourself how you can play with AC diagnosis and repair while being too cheap to get a real set of service gauges.....do you have a vacuum pump? Wrenches?


I'm through with this topic, keep plodding through with partial information.

mk378 on Thu November 12, 2015 7:12 PM User is offline

The answer to your original question is yes, any time you disconnect a line to replace a part, the system will fill up with air, and you need to pull a vacuum to remove that air before recharging. Trying to run a mixture of air and refrigerant will have poor performance.

It is also possible for a TXV to get sticky and stick closed, even though there is not a freeze-up. It takes a LOT of water to freeze the expansion valve, like a car that was in a flood or had an A/C line left open for a time and not properly decontaminated.

There are pressures lower than zero psig, a cheap gauge will not show that.

bohica2xo on Thu November 12, 2015 8:41 PM User is offline

Quote
Originally posted by: peanutaxis
Hi,


My question is, do I really need to go to the prohibitive expense of buying or paying someone to vacuum out the system to boil the moisture off?

p

If you consider the most basic part of servicing the system to be cost prohibitive, you should stop working on it.

The system needs to be evacuated to remove the non-condensing gasses from it.

Servicing an A/C system requires some specialized tools. Trying the job without them ends in failure, and can be dangerous.



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