A/C recharge

[greenskeeper]

I'm not a fan of A/C but the wife and 2yr old son have different opinions

 

[rotarykid]

I have been using leak sealer charges for over 30 years without ever having a problem. I have used these charges to stop leaks in refrigerant lines, to seal dried out on O-rings, and even stopped leaks on the main seal on the compressor. If you follow the directions they work very well in swelling dried out O-rings that have leaked. There are even some sealer charges that contain a resin epoxy that can patch a leak in the coil of a evaporator and condenser. All this scare tactic of saying never use them is a pointless waste of a tool that many times can repair an ac system for years.

I speak from repairing over 200 auto ac systems in the last 30+ years. Many times when you start to repair a known issue in an older ac system the breaking of the system open to air causes new failures. Using a stop leak charge as I stated earlier can prevent other failure from happening during the repair.

 

[sfierz]

Good point, Rotary. No need to be causing more problems while we are trying to fix other ones. On the other hand, no need putting needless chemicals into a system that doesn't need it and may cause problems down the road if the system didn't need the stop leak sealer, etc. etc. and it gums up the works. The purist sage A/C advice here has saved me money and trouble by allowing me to recharge old systems without putting in needless chemicals in unknown amounts. On the other hand, if a leak sealant helps an old system then use it, by golly.

I have been using leak sealer charges for over 30 years without ever having a problem. I have used these charges to stop leaks in refrigerant lines, to seal dried out on O-rings, and even stopped leaks on the main seal on the compressor. If you follow the directions they work very well in swelling dried out O-rings that have leaked. There are even some sealer charges that contain a resin epoxy that can patch a leak in the coil of a evaporator and condenser. All this scare tactic of saying never use them is a pointless waste of a tool that many times can repair an ac system for years.

I speak from repairing over 200 auto ac systems in the last 30+ years. Many times when you start to repair a known issue in an older ac system the breaking of the system open to air causes new failures. Using a stop leak charge as I stated earlier can prevent other failure from happening during the repair.

 

[greenskeeper]

a/c leak sealer is nothing like "bars stop leak" for radiators, which I think people associate as the same type of fix when they are completely different in the way they work.

 

[greenskeeper]

all new o-rings, new receiver/dryer

I put 1 can (12oz) of refrig into the system (way low I know) and pressure was only 25psi at 80F (again, way low)

I had cold air for about 5 minutes and then the compressor kicked off. The low side pressure is way too high. It pegged the gauge.

If I let the car sit for 5-10 minutes and turn the a/c on the pressure drops back to 25psi and the a/c works cold again.

I am hesitant to add more refrig to bring it up to the correct pressure since isn't cheap, unless that is causing the problem.

I can't see how there could be a restriction in the lines as I took everything off, blew everything out with air.

Only other thing I can think of is if something is icing over and causing a temporary blockage?

 

[sfierz]

Low side pressure should be higher than that, IMHO. I'm thinking 35-40 PSI and then the high side pressure should come down. There is an inverse relationship between the two. If the low side pressure is too low the compressor will not come on.

 

[rotarykid]

The 38-40 to 55 psig low side and the high side should be ~150-200 to 450-500 psig when operating depending on ambient temps is right out of the refrigerant install/refill manual for HFC-134a . 55 psig is the bleed down starting point on the high end of the bleed down scale ( hotter side ) , 38-40 psig is at the low end of the scale ( cooler side ) if the system is filled to the correct level. In a properly operating and filled HFC system the pressure should start to cool @ ~ 55-58 psig on the low side. As the system removes the heat from the car the low side pressure should drop down to the mid 40s psig range .

If the system is under filled you will see readings below 35 psig, below the bleed down valve opening pressure so little to no cooling . A reason for a high reading of ~55 psig can be a moisture clogged dryer/receiver not allowing for bleed down . The system can build higher pressures to force the charge through the slightly clogged dryer/receiver on it's way to the evaporator. Another reason for a high pressure reading on the low side is a system being overfilled . Also if the expansion valve is either stuck closed or open low side pressures will be out of the cooling range.

An overfilled HFC system will not cool and can lead to an overpressure, above 500 psig on the high side. Once the pressures reaches this point a compressor failure can happen if the overpressure valve doesn't open or a hose failure is likely. It is very easy to reach the overfilled point on an HFC filled system if not filling from a vacuum. The most common reason for an overfill is a system that was filled not under a complete vacuum. As long as the system can get into that range of 40-55 psig low side with the high side at least 200-400 psig the system can cool. But if you are stuck in the higher end of that scale range on the low side the system can be less efficient during extreme heat shock.

I have seen systems have to be filled then drained then filled again to get a HFC-134a charge correct. I even saw this happen once in a class I took in college with the teacher following all the correct procedures. HFC-134a filled systems have a very small operationaly system volume window for correct operation. Even when everything is correct and in good working order recharging the system can be tricky to get right.

 

[greenskeeper]

I'm going to try and vacuum the system again and recharge after replacing the expansion valve.

After that if it still doesn't work then I give up.

 

[sfierz]

I'm telling you, it will take more than one can of R134a. Look at your individuals car specs for the A/C system but I am guessing, when empty, it will take more than that. Low side, when cooling, should be in the 35-40 range.

 

[greenskeeper]

I'm telling you, it will take more than one can of R134a. Look at your individuals car specs for the A/C system but I am guessing, when empty, it will take more than that. Low side, when cooling, should be in the 35-40 range.

o-ring fail
going to replace all o-rings and the dryer/accumlator
see what happens then.
from my research the system should take 28oz of ref and 3.9oz of oil if completely dry.

I know it takes more than a can, don't want to waste r134 since it isn't cheap!

 

[sfierz]

Yeah, it did go up. Used to be $6.99/can here. Now it is $9.99/can for the basic stuff without leak sealer. If you are starting with all new o-rings and receiver dryer I would think that you can use the basic stuff plus the correct amount of PAG oil. I bet your A/c will take 2-3 cans of R134a.

I know it takes more than a can, don't want to waste r134 since it isn't cheap!

 

[greenskeeper]

cheapest around here is $14.99 for a 10oz can of straight r134a

 

[sfierz]

Ouch. The cans here are 12 oz I believe and $9.99 at Blain's Farm and Fleet.

cheapest around here is $14.99 for a 10oz can of straight r134a

 

[Project-TDI]

I'm not seeing your logic here. You complain about not wanting to "waste" more freon. Yet you are going to vac the can you just put in and start over. You need to add more freon to keep the clutch kicked in. With only one can, as soon as the clutch kicks in the pressure will drop to around 20-25. Your low pressure switch will kick out the clutch as a safety mechanism for several reasons, one of them being the logic if freon was lost then it would be possible to lose oil as well- starving the compressor. The liquid line will also freeze at too low of a pressure. Of course all of this is pressure controlled, as it is more accurate than an actual temperature sensor that would be affected by ambient air. It will not keep continuously engaged until the latter end of the second can, assuming it holds a little over two cans. Typically it will kick in and out less frequently as you add freon until eventually it does not kick out at all. To speed up the rate at which the system accepts freon, you can set it into a container of warm (not hot) water to keep it from freezing up. NEVER turn the container upside down. On a receiver/drier system such as ours you do not want solid liquid entering the line. I suppose on an accumulator you could but I dont see the benefit. You are also going to want to run it for quite a while to make sure it has stabilized (once the evaporator has removed ambient heat from the cab down to a stable temperature), or if you have a means to weigh the freon such as a postal scale: just insert the exact amount stated on the label under the hood in kG. All that being said, can someone please chime in on the proper pressure assuming we arent starting with an empty system (for the original poster's sake as well as my own)? I have an 03 Jetta Tdi. Ambient temperature when I get home is usually 100-105 and does not cool down until after midnight. I have tried between 38 and 52 psi low side, just can't seem to get it quite right. Perhaps a chart that would be useful? All I can seem to find online are generalized charts and VW vehicles seem to run a little less.

 

[d2305]

http://aircondition.com/

 

[greenskeeper]

A/C runs cold for about 6-7 minutes then the compressor shuts off due to the high pressure shutoff switch. The low side gets over 100psi.

This leads me to think I either have icing causing a blockage or a bad expansion valve (stuck open)

If I let the car sit a while, the A/C will work again for about 6-7 minutes, which further makes me think it is moisture icing in the system.

 

[Gearhead51]

Are you sure it's high pressure and not a low pressure switch? I'm sure the system has low pressure switch, or a transducer that reads temp which can function as both. I haven't done much work on my Jetta, but I have trained quite a few people how to do basic troubleshooting. Are your fans running properly? If the system runs too low a pressure, the compressor will kick off. Many auto A/C systems also have a frost "sensor" on the evap. If they get too cold, they will shut off the compressor to keep it from turning into a block of ice from humidity freezing on it. Both are signs of low refrigerant charge. I think you need to add more freon, but without knowing your high side pressure, you are running in circles. The proper way to charge auto A/C is with a digital scale. The new J2788 spec required measurement to hundreths of a pound and 3% or 5% error, if I remember correctly.

 

[greenskeeper]

Are you sure it's high pressure and not a low pressure switch?

the low side shouldn't be over 100psi correct? More like 55psi according to my chart. when the A/C stops working (compressor kicks off) the low side reads over 100psi.

 

[compu_85]

What is the low side reading right before the compressor kicks off?

-J

 

[greenskeeper]

What is the low side reading right before the compressor kicks off?

-J

low side was down to 15psi or so.

I added some more refrig to bring the pressure up to reference the chart for 90F

I never got the presssure high enough according to the chart, now the compresssor cycles on and off repeatedly.

overfilled? even though I was well below what the chart said for 90F (around 45psi actual, chart said 55psi).

 

[sfierz]

That doesn't sounds overfilled to me. I've had my air happily running with a PSI low side around 40. I think you might have a bad expansion valve. It should not be this hard to get this thing running and keeping correct pressure. Otherwise, you may have a faster leak and it is not letting the system come to pressure at all. You really need to get some gauges on there and see what it going on. How does the compressor sound when it is running? Have you added any PAG oil in addition to the freon?

low side was down to 15psi or so.

I added some more refrig to bring the pressure up to reference the chart for 90F

I never got the presssure high enough according to the chart, now the compresssor cycles on and off repeatedly.

overfilled? even though I was well below what the chart said for 90F (around 45psi actual, chart said 55psi).

 

[compu_85]

Ya, the system sounds underfilled.

-J

 

[greenskeeper]

That doesn't sounds overfilled to me. I've had my air happily running with a PSI low side around 40. I think you might have a bad expansion valve. It should not be this hard to get this thing running and keeping correct pressure. Otherwise, you may have a faster leak and it is not letting the system come to pressure at all. You really need to get some gauges on there and see what it going on. How does the compressor sound when it is running? Have you added any PAG oil in addition to the freon?

no leaks, bad o-ring and I replaced all of them while I was at it.

any way to bench test the expansion valve?

will also get a new set of gauges, i think mine are funky.

 

[Project-TDI]

How much freon have you actually put into the system so far? The system will not stay engaged constantly until your second can or so. They take slightly over two cans. For example, if you had only one can in the system, the compressor would engage and the pressure would drop to 15 psi. This triggers the low pressure switch, and when the compressor shuts off both sides should equalize anywhere from 70-110psi. If you had a real set of gauges (I assume you are using only the low side) you would see both sides match when the compressor is not engaged. I am afraid you are over thinking this, no offense.

 

[greenskeeper]

emptied system

vacuum pump for 5min, 28" of vacuum

shut of pump, waited 10 min, still 28" of vacuum

now I am going to run the pump for 30min to an hour

So, what should my readings be when "full" on the low and high side (while running), based on 90F ambient temp?

 

[DPM]

fill by weight.

 

[greenskeeper]

so 28oz refrig, 3.9oz oil as per bentley?

 

[greenskeeper]

the brand new receiver/dryer was defective (leaked, although not all the time, weird) which I got from a source I use quite a lot. Disappointed but it happens.

New (2) receiver/dryer in place. Held vacuum overnite so I should be able to charge this morning once I get home from work.

"cross fingers"

 

[sfierz]

Charge it up proper and it should work. More than 15 PSI low side, more like 35-40 PSI. That should get the A/c pumping.

the brand new receiver/dryer was defective (leaked, although not all the time, weird) which I got from a source I use quite a lot. Disappointed but it happens.

New (2) receiver/dryer in place. Held vacuum overnite so I should be able to charge this morning once I get home from work.

"cross fingers"

 

[DanG144]

DO NOT add refrigerant to a target pressure.

Add only the recommended volume of refrigerant and oil (oil is tricky to calculate).

Mk IV compressors will cycle off on high pressure. Which it sounds as if your Mk III was doing.