Drew's AC woes (72F)

[Stephen Rice]

So tonight Drew came over to have a little AC work done.  Let me start by telling the AC history of his car.

Last summer he dropped by my house telling me how his AC didn't work.  We spent that evening concerting him to r134a and he left pretty dang happy.  His mode switch wouldn't work in the max position but he was still getting 48 degree vent temps with his AC switch in the normal position.  He left my house smiling and we never did get around to fixing his mode switch.

Over the past year we have topped off his AC system once or twice.  This summer he mentioned it not being as cold as it used to be so I suggested that we look into repairing his mode switch.  His AC simply wouldn't blow any air out of the vents at all when the switch was in the max position. 

We removed his switch and replaced it with mine for testing purposes.  Suddenly his AC blew air out of the vents with the switch in the MAX position.  We put a thermometer in the front vent and only got 80F temperatures.  Drew went for a drive on the interstate and the temp slowly crawled down to 72F.

Before his drive I checked the pressure on the low side.  He is getting 100 lbs with the car not running.  With the car running he was getting 35 lbs with the car idling.   We gave it a little extra r134a boosting it to 40 lbs of pressure.  With that he is only getting 72F on the interstate.

Are there any suggestions on what to do?  I really don't suspect him being low on refrigerant since he had 100 lbs with the engine shut off.  Could it be the AC compressor?  The clutch is engaging.  He has a new compressor we could install if necessary.

-Steve Rice
#16510

[Bill Robertson]

You want lower low side pressure, not higher. Higher pressure makes it harder for the freon to "boil" (turn into a gas). 45 PSI is the marked upper refrigeration threshold on my low side gauge.

Put a gauge on the high side. If the high side is not climbing into the 200's, Drew is either low on freon, the compressor is cycling off too quickly, or the orifice tube isn't restricting freon into the evaporator.

Depending upon outside temp, 100 PSI static may be too low. 100 PSI rest pressure is only normal when it's in the 80's. In the 90's it's usually closer to 110-120. Higher temps and higher pressures go hand in hand (conversly, lower temps and lower pressures go together -- hence the 25 PSI low side refrigeration standard).

Note that outside air in the system will give false readings. If Drew's A/C leaked down to atmospheric pressure during the winter, his system is contaminated with outside air and needs to be revacuumed. Outside air does not turn into a gas in the evaporator, and gives higher low side readings than uncontaminated freon.

Also, do not use the "Normal" mode switch setting. That draws hot humid outside air into the cabin, just like leaving your household windows open while running central A/C. "Max" recirculates already cooled and dehumidified air -- much more efficient.

Bill.

[Stephen Rice]

Gotcha.  My guess is he is low on r134a but I didn't want to put too much in it and blow something up.  We flushed out his system last summer so the orifice tube should be fine.  So is it safe to add a can or so to the system if the high side is around 100 lbs or so?

We didn't put a gauge on the high side tonight but I can do that for him Sunday evening.

-Steve Rice
#16510

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[Bill Robertson]

I'd throw away whatever is in it, pull a fresh vacuum, then recharge with some of that cheap freon you're bragging about. If his system got contaminated with outside air it'll never work right.

Bill.

[Stephen Rice]

That wouldn't hurt.  It would be cheaper than possibly popping a hose.  I think Drew still owes me some cash for the last few cans of r134a.  My inventory currently consists of $8 cans.  I have to get rid of that stuff before I can start buying refrigerant at Sams club.

-Steve Rice
#16510

On Thu, Jun 27, 2013 at 10:32 PM, Bill Robertson <brobe...@carolina.net> wrote:

I'd throw away whatever is in it, pull a fresh vacuum, then recharge with some of that cheap freon you're bragging about. If his system got contaminated with outside air it'll never work right.

Bill.

[Bill Robertson]

Just don't give any of it to Brandon -- that's my turf.

Before recharging Drew's system flush it out first. Any opportunity to clean the orifice tube is good.

I eventually traced my leak to the low side pressure switch. The housing is made of steel and rusts pretty badly.

Bill.

[Drew]

Drew doesn't pay Steve in cash. Only Popeyes and Chinese buffet. 

Drew

[stev...@gmail.com]

He tried bribing me with Chic Filet last night but it didn't work.  

Steve Rice

#16510