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dolphins
Clean Up Our Oceans
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join:2001-08-22
Westville, NJ
kudos:7
Reviews:
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1 edit

[Help] AC Pressures

2000 Lincoln Town Car. I filled it with R-134A to 45psi @ 78 degrees F ambient temp about a month ago. It's already blowing warm air.

Engine off, pressure equalized, ambient temperature 74 degrees F:




Short video of pressures while compressor is cycling.
downloadMovie.wmv 3853785 bytes

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Beezel

join:2008-12-15
Las Vegas, NV

said by dolphins:

2000 Lincoln Town Car. I filled it with R-134A to 45psi @ 78 degrees F ambient temp about a month ago. It's already blowing warm air.

Engine off, pressure equalized, ambient temperature 74 degrees F:
[att=1]

Short video of pressures while compressor is cycling.
[att=2]

First of all you say you are using R-134a, well your guages are not for R-134a. They are for R-12, R-22, etc. So your readings won't be accurate. So there might be your problem. Plus you should recharge by weight for accuracy.


dolphins
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Yes, I know the gauges are old. I had to retrofit the gauges with R-134A quick connects. Without researching it myself I was told that the replacement for R-502 (the outer most scale in black) was similar in properties to R-134A and can be measured the on the same scale.
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Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to Beezel

All that matters on a gauge is the pounds. A PSI is a PSI. Ignore the temperature scales if you're not using one of those refrigerants. (And don;t use those on a 410 system.

I cannot see your video for some reason, keep getting an error. What do the pressures read when the clutch is engaged and running?



dolphins
Clean Up Our Oceans
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join:2001-08-22
Westville, NJ
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Thanks Buddy,

I converted it to .wmv so you should be able to view it now.



Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4

You are undercharged. Leak somewhere.



dolphins
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Westville, NJ
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That's what I told the mechanic out at Holman Ford. They put the dye in it and couldn't find the leak.
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TheHarvester
Premium
join:2006-08-25
Dana Point, CA
kudos:3

It would be a sizable leak to lose that much refrigerant in a month. Also, the system needs to be used for the dye to mix with the oil and the oil/dye to get to the leak.
If you have access to a standard black light you can search for the dye yourself as it should light up nicely with a black light.
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Lurch77
Premium
join:2001-11-22
Oconto, WI
kudos:4
reply to dolphins

Don't forget to check the service ports with the gage set removed. I have seen the lines rub through where contacted other metal, and, as big a pain in the ass it is, you need to tear the dash apart and check the evap coil and connections.



dolphins
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I was just reading where the evaporator is located. Crap, that's probably where the leak is since no one can find it.

My thanks to both of you.

I'll be sure to update when I find the leak.
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TheHarvester
Premium
join:2006-08-25
Dana Point, CA
kudos:3

It is possible to find evap leaks without tearing the dash apart. If you can see the drain hose, sometimes the dye will show up inside the tube or on the firewall where the water drips down. Another way is to put a piece of cotton ball inside the tube, it will trap some of the dye in the cotton and you can check it. Remember, the system needs to be used to help get the oil to the leak. Also, adding some oil to the system may not be a bad idea as well.
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dolphins
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Just realized I wasn't subscribed to this thread anymore after the ole switcheroo.

I did go over the engine compartment with a black light but found nothing. The only place I saw any bright neon greenish yellow residue was on the low-side tap and accumulator which is consistent with the recent recharge. I did it at night so the whole engine compartment was illuminated in black light. FYI, bugs love black lights. It's time to find a AC tech and not just a mechanic. Even if I do find the leak, I don't have the equipment to do the repair.

I'll post back when it's fixed.
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Master5c8

join:2002-09-15
Urbana, IL

Valve cores can fail and leak. How much dye leakage were you getting from the low side service port? You could also attempt to clean it and see if the dye reappears.


torch

join:2009-04-30
P1H 3J4
reply to dolphins

You cannot fill an AC system by pressure. The static pressure (ie: engine off) will be the same if there is one ounce of liquid as with 20 oz of liquid -- the static pressure is the vapour pressure of the liquid at a given temperature. It varies by temperature, not by quantity. The cooling capacity varies by the weight of liquid in the system and you cannot determine that by pressure.

At 78°F, the vapour pressure of R134a is 83 psi. Your static reading shows you had at least a little liquid in the system.

With the system running, a CCOT type R134a system low pressure will cycle between around 20 psi and 40 psi. As the compressor runs, the low side pressure drops, chilling the liquid refrigerant. When it drops below freezing, the evaporator fins could freeze over, obstructing air flow, so the low pressure switch cuts off the compressor, allowing the temperature to rise back up above freezing.

At 78° it may not cycle at idle -- these things should actually be checked at 1500 to 2000 rpm -- whereas your video seems to show a rapid cycling typical of much lower ambient temperatures, a drastic undercharge or an obstructed orifice tube. The car sure isn't going to cool well when cycling that fast. If the system was as undercharged as that rapid cycling at idle suggests, it wouldn't have to leak very much to quit completely. BTW: Don't run the AC when undercharged like that -- the refrigerant circulates the oil so you are starving your compressor of oil.

Since you can't find a leak, have the system evacuated, vacuumed and recharged by weight (as indicated on the underhood sticker). See if it cycles normally after that. Then get an electronic leak detector and track down any leakage. Since you can't find it visually, there's two likely places. First, put the blower on low and check the vents inside the car. If the evaporator is leaking that's where you'll get a hit. Second, take the fan belt off and put a plastic bag around the compressor overnight. If the detector reacts to the bag contents in the morning, the shaft seal is leaking.



dolphins
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Westville, NJ
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reply to dolphins

My thanks to everyone for the help. It's now someone else's headache. I decided to trade it in for a 2012 Chevy Malibu LS.
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