advertisement
Deals | News | Forums

The Forum is sponsored by 
 

AAPL stock: $98.38 ( -0.64 )

*Cached every 60 seconds. For live updating, Click Here

You are currently viewing the Tips and Deals forum
Car Guys Question: Auto AC blows cold, then warm
Posted by: cbelt3
Date: June 08, 2010 07:44AM
Honda Civic 2002- AC will start off OK, then blows warm air after ten minutes or so. Checked the charge with the cheapo 'refill kit' and it was OK.

Google search says it sounds like a water contamination in the system is causing expansion valve freeze-up.

Is it safe to assume I'd need to take it in for a 'flush and fill' of the system ? I assume they put a vacuum to the lines to empty it out and dry it out, then refill with a bit of oil, leak detector, and R134a.

I'd rather 'do it myself', but I don't think it would work.... venting the system by opening the high pressure bleed valve into the air and then refilling would probably not get all the moisture out of the lines ?
Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: olnacl
Date: June 08, 2010 07:54AM
You are correct in the assumption that opening the system to the atmosphere will not get the moisture out. You have to pull the closed system down into a vacuum low enough for the moisture to boil and be discharged by the vacuum pump. This will take an hour at least after being pulled down. You should also replace the receiver/dryer immediately before attaching the vacuum pump.

Added a link.







Edited 1 time(s). Last edit at 06/08/2010 07:56AM by olnacl.
Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: cbelt3
Date: June 08, 2010 08:43AM
Hmmm.... Vacuum pumps are available for cheap.. the venturi type, not the cryogenic type big grin smiley

Hmm. Maybe I CAN do this myself. Good advice on the dryer assembly. Carp, those are like $80. I'll ask my favorite car repair shop about the cost overall.
Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: mrbigstuff
Date: June 08, 2010 08:58AM
I do a lot of home mechanic-ing and I would not even attempt something like this. Of course, for the mad scientist type who sees it as a challenge, I understand. But the shops just hook it up and since most AC units are fairly standardized nowadays, I don't believe it takes much time. For my older car this cost about $129, IIRC, last year. They injected dye along with charging the system, let it stay for a couple of hours and looked for leaks (they didn't find any).
Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: Carm
Date: June 08, 2010 11:10AM
olnacl is right on the money.
Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: olnacl
Date: June 08, 2010 11:36AM
Here's a chart on how much vacuum to pull to boil off any water in the system, and the web page with more answers.

At sea level, water begins to boil and change into a vapor state at 212 degrees Fahrenheit. If we increases the pressure we can raise the boiling point of water. An example of this would be the typical automotive cooling system which uses a 15 lb. radiator cap to maintain a design pressure. In that system, the idea is to raise the pressure and therefore raise the temperature at which the cooling liquid will boil. If we wish to lower the boiling point of liquid, we simply remove the pressure that's on top of that liquid. That's how we boil water out of an air conditioning system. We use a vacuum pump to bring the system to a level of near perfect vacuum so the water will boil off and be carried away as a vapor. It's important to note that ambient temperature has much to do with the point at which liquids will boil under vacuum. The greater the temperature, the fewer microns of vacuum will be required to start the boiling process. If you've been keeping note, you know that non condensables (air) and moisture are two things you definitely don't want in your a/c system.
The chart below shows how temperature plays a role in the level of vacuum needed to boil water.


Bottom line is that if you can't pull enough vacuum to get the water to boil at your altitude, you have a leak in the system (or a lousy vacuum pump).



Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: guod
Date: June 08, 2010 01:56PM
I had an issue similar to yours several years ago. (probably about 10 years ago)

Mine turned out to be an electrical problem a previous garage had damaged a wiring harness going to the compressor. The fan kept running, but the little light on the dash that indicated if the A/C was on or off would sometimes be on, and sometimes off. After the new garage repaired the harness, the A/C light was always on and blowing cold.

It might not be your issue, but I'm just adding my 2 cents. but if your charge is good..............................



Options:  Reply • Quote
Re: Car Guys Question: Auto AC blows cold, then warm
Posted by: Dick Moore
Date: June 08, 2010 11:13PM
Or it's just a faulty thermostatic expansion valve. Either way, take it to a pro.



What it is, man, a low-down and funky feelin'
Options:  Reply • Quote
Sorry, only registered users may post in this forum.

Click here to login