AC High side & Low Side Pressures

maschwar

Well-known member
Joined
Feb 19, 2003
Location
Fayetteville, Ga
TDI
Jetta, 2003, silver
I have a 2003 Jetta TDI with 262,000 miles and will be replacing the AC compressor, drier, and expansion valve. I'm replacing the compressor due to noises that I'm hearing with the AC on and I'm seeing oil up under the compressor so I beleive its seals are leaking oil. I will pull a vacuum on the system for a hour to dry it out after reinstalling the new compressor drier and expansion valves. I would like to know what the high side and low side pressures need to be for a full charge on this system. If I understand correctly, the system takes 750 g of R-143a but would like to know the pressures I can expect to see.

Also can someone ginve me some tips on loading the gas back into the system, and some pointers..

Thanks :)
 

maschwar

Well-known member
Joined
Feb 19, 2003
Location
Fayetteville, Ga
TDI
Jetta, 2003, silver
Need to also know which is the high side coupling and which is the low side coupling on the car hoses The test gauge couplings seem backwards,, the blue low side coupling fits on the front hose fitting by the radiator and the red high side gauge coupling fits on the rear port at the fire wall.. Is that correct? I have read on the forum that the low side on the car is the hose by the firewall and the high side is by the radiator?
 

Bran Diezel

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Joined
Jul 13, 2009
Location
Bristol, Va
TDI
On my 5th TDi - 2003 ALH 5spd Wagon
Low is up front.

Small fitting = low side
Large fitting = high side

You prob need to read a few articles on how ac works and what different pressures can mean before you dive head first.

You can find a chart for static pressures too, but remember numbers are just numbers, they won't tell you if any air is in the system, refrigerant is contaminated, how much oil is in the system, etc.
 

sackman

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Jul 30, 2009
Location
Oregon
TDI
2(2003) 2Dr ARL/ASV
It's pretty simple, fill on the low side up front, you can also look up how many oz of refrigerant the system takes and just fill to that amount.

If memory serves it is 28 oz , you'll have to look it up unless someone on here wants to chime in.

Just don't do this in front of the police as it is illegal to release refrigerant into the air without being contained/removed.
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
You need to drain and measure the oil in the old pump. Drain the case and turn it on end and drain the head.

Drain the new pump.

Add the amount that was in the old pump back into the case of the new pump plus the amount that the drier holds. Can't remember that amount but you can probably search it up here.

To charge it what I do is set the full can with the hose hooked up on a scale and record the weight.

Open open the low side valve and the charge valve on the end of the hose. Put the can in a tub of hot water. It'll boil out and you can get the whole can in. Shake it to make sure it's empty.

If the target is 28 oz as stated above, repeat with a second 12 oz can for a total of 24 oz.

Hook up a third can and feed in 4 oz using the valve on the can. Little at a time. Really only need to get the full weight on the last can before opening the valves. When trying to weigh the last 4 oz in make sure the hose is hanging the same as it was when full. You are trying to duplicate the effect of hose on the weight reading. Close only the valve on the can.

Since this is going in the low side and there is possibly liquid in the pump I turn it over by hand a bit to make sure it isn't locked up.

When satisfied any liquid is out of the pump start it up and let the pump draw down the pressure on the fill hose to the minimum of around 30 psi before closing the valve on the manifold so all the liquid in the hose boils off into the system.

This is how I do it with small cans. I get the full charge in before starting it. There's some inaccuracy due to the hose but I figger it's close enough. Could disconnect the can each time for weighing but you loose some gas each time you disconnect and that prolly would cause more error than the weigh I do it.
 
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sackman

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Jul 30, 2009
Location
Oregon
TDI
2(2003) 2Dr ARL/ASV
Figured I would update this thread since I just had to change out my Valeo Radiator Fan, which failed after 17-20k miles of use... Only buy Febi brand radiator fans.

Since I was down there I hooked up the gauges to see what my readings are with the compressor on and off.

A year ago I vacuumed out and filled the system putting exactly 28oz in. I weighed the last 12oz can on a digital scale, stopping when it dropped by 4 oz.

So here are my readings a year later.


Compressor Off:



Compressor On:
 

Jesse_Boyer

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Joined
Aug 16, 2007
Location
Sioux Falls, SD
TDI
I'm all out...
That's what I assume you'd see as well, around 30psi and near 190psi given a 75F ambient temperature. (Another rule of thumb for the high-side is 2.5 times the ambient temperature (or 190psi in this case.)

What do you see for vent temperatures?
 

sackman

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Jul 30, 2009
Location
Oregon
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2(2003) 2Dr ARL/ASV
That's what I assume you'd see as well, around 30psi and near 190psi given a 75F ambient temperature. (Another rule of thumb for the high-side is 2.5 times the ambient temperature (or 190psi in this case.)

What do you see for vent temperatures?

Unfortunately I don't have a thermometer to give you guys a scientific reading, but when I hold my fingers covering the vent it is uncomfortably cold, I'd guess mid to high 30s..?

My cabin blower fan doesn't put out the air volume as the other tdi I have, I'm thinking I've got a bad resistor, but looks like guys have had the fan or fan bearing go bad resulting in similar issues.

But I can confirm that the Ac compressor kicking on is dependent on what fan speed setting you have it on, I notice it kick on with about half the frequency in position 2 as opposed to 4.

So unfortunately that means with the fan putting out less volume it seems that I am running my compressor excessively by having the fan in position 3/4 most of the time to stay cool. :cool:
 
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Enabled

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Apr 23, 2013
Location
Houston, TX
TDI
2003 Jetta TDI Manual, BMW 328d SW
I thought these compressors don't cycle on/off but rather modulate the flow through the refrigerant control valve?
 

Jesse_Boyer

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Joined
Aug 16, 2007
Location
Sioux Falls, SD
TDI
I'm all out...
Unfortunately I don't have a thermometer to give you guys a scientific reading, but when I hold my fingers covering the vent it is uncomfortably cold, I'd guess mid to high 30s..?

My cabin blower fan doesn't put out the air volume as the other tdi I have, I'm thinking I've got a bad resistor, but looks like guys have had the fan or fan bearing go bad resulting in similar issues.

But I can confirm that the Ac compressor kicking on is dependent on what fan speed setting you have it on, I notice it kick on with about half the frequency in position 2 as opposed to 4.

So unfortunately that means with the fan putting out less volume it seems that I am running my compressor excessively by having the fan in position 3/4 most of the time to stay cool. :cool:

As I understand it, the poster above is correct. The compressor is always engaged (with the AC on) and modulates refrigerant via the refrigerant control valve.

Regarding fan performance, does the fan speed 'sound' actually change when you change the fan speed position?
If the cabin air filter is clear and the fan speed ramps up/down appropriately, you're looking at an airflow direction issue. With proper foam on blend doors sealing to the housing, a clean evaporator, and clean filter, the fan might blow your hat off on setting four. It's a ton of air flow compared to most other cars I own.

Also, at mid/high 30's, that's perfect and you may not get much better than that. The coldest of the ALH's I've owned was 38-39F on fan setting one and that has been impossible to replicate with the current 02 ALH.
 

DanG144

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Joined
Aug 2, 2007
Location
Chapin, South Carolina, USA
TDI
2005 A4 Jetta 5spd
If your AC clutch is actually disengaging, cycling, that is VERY unusual in these cars. That would mean something is wrong.

1) Your clutch would cycle off at 350 psig and back on at 250 psig high side refrigerant pressure, if your radiator fans were not cooling enough, or if you had the system badly overcharged. If it is badly overcharged, you can end up damaging the system badly. Fast speed fans come on around 250 psig or so.

2) Your AC clutch would cycle on and off if you had a problem with overheating, or if your ECU thought it was overheating due to a bad temperature sensor.

3) Your AC clutch can be cycled off at very high power demands by the ECU.

All 3 of these are very rarely a problem. When everything is going correctly your AC clutch does stay engaged continuously.

Perhaps you are feeling something else?
 

DanEboy

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Joined
Mar 26, 2003
Location
Commack, NY (Long Island)
TDI
Jetta GLS 2000 Auto
I know this is an older thread... but,
Isn't there a low pressure switch also?
And if the pressure was on the low side couldn't that also cause the compressor clutch to cycle on/off?
Anyone know what the low pressure switch value is?
 

rrgrassi

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Joined
Jul 31, 2006
Location
Royse City, TX
TDI
'06 Jetta TDI 5 speed
The OP did not mention attaching a vacuum pump the evac the system. So always evec before refilling. BG fridgi-quite is a very good oil to use as well.
 

Mongler98

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Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
the work you are going to do is much more involved than you think.
key words you need to do the job that no one really tells you about
Nitrogen
keep the dryer purged
flush
be supper anal about your PAG oil, dont trust nothing
 

JimInPB

Active member
Joined
Feb 3, 2019
Location
Florida
TDI
1999.5 ALH Jetta
99.5 Jetta ALH with a Chinese AC compressor that I put in about 3 years ago, was putting out air at less than 30F on hot days (85+F) with the fan set to 3 or 4 and got down closer to 20F when I had been driving for a very long time & the temperature in the cabin was cold enough to fog my glasses when I got out of the car. This was with the air intake vent on recirculate. It would reliably reach these temperatures in less than 5 minutes. I had done the blend door fix several years ago.

Yesterday I had a sudden decrease in performance. It struggled to get down to 40f after driving for 25 minutes. I checked the hot side fan. It was running. I didn't remember what pressures the AC system used to run & I couldn't find my notes, so I drained what was left of the refrigerant into scrap cans & loaded from vacuum. My VW factory tag says R-134a 750g +50. That means 28.25 oz max & about 26 min. I charged 26 oz. I'm still seeing 40f at best. I now suspect a plugged receiver/dryer or a degraded control valve. I'll see if I can get a receiver/dryer tomorrow. If that doesn't work, then I'll look into a new valve. I think that I used a cheap Chinese valve when I put in the new compressor, but I remember getting a better quality dryer because the Chinese one was just obvious junk.

My low side pressure readings were around 25psi & the high side was running about 250psi with an ambient temp around 80F. Those pressure numbers look pretty darn good to me. That's why I'm thinking that I likely have a blockage somewhere. I didn't inspect the plumbing yet, but I suspect that I'm seeing high side pressure before the receiver & the condenser is likely seeing less.

When you run the outlet temperature below 30F in a humid environment, the low side (evaporator) ices up after about 30-45 minutes & you loose air flow. At that point, you need to shut off the AC button & let warm air blow over it for a couple of minutes to get air flow back, then push the AC button again & it's back to being like a meat locker in there. If you go to places where it's dry & an average warm summer day is 110F (like Phoenix or Las Vegas) a tune like that makes sense. In a humid place where the summers don't normally top 100F, then 33-38F at the output side makes a lot more sense. You can reach those numbers with a Jetta if everything is tuned up correctly.

Dryers are extremely important. If moisture gets into the system, it reacts with the PAG oil & forms an acid that results in "the black death" covering the entire inside of the system. This is why you want to pull a full 30mm of vacuum on the system before charging it. Strong vacuum removes the last traces of free moisture.

Edit:
Actually, on second, thought, I'm going to look back into the blend door & the low side plumbing first. 25psi on the low side should give me very cold air. It's the low side pressure that determines the outlet temperature. I'm seeing good low pressure at the low pressure port but I'm not seeing low enough temperatures at the dashboard register. The problem is likely between those two places.
 
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Genesis

Top Post Dawg
Joined
Feb 26, 2003
Location
Sevier County TN
TDI
'03 Jetta Wagon
The TXV should prevent you from having an evaporator core below freezing temps. That's THE JOB it is supposed to do.

If you're getting temps under 40F or so at the outlets and the charge is correct the TXV is defective. Replace it.
 

AndyBees

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Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Isn't 45 psi suction side and anything over 200 psi on pressure side the norm for 134a at about 85f ambient?

There is a refrigerant charge level (low) that will result in very cold temps to the point the evaporator will freeze up.
Then, it got too low to provide cooling. But, seems the pressure switch would have kept the compressor from kicking-in.

Both fans out front should spin when the AC is On.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
Isn't 45 psi suction side and anything over 200 psi on pressure side the norm for 134a at about 85f ambient?

There is a refrigerant charge level (low) that will result in very cold temps to the point the evaporator will freeze up.
Then, it got too low to provide cooling. But, seems the pressure switch would have kept the compressor from kicking-in.

Both fans out front should spin when the AC is On.
No way. That's not even a valid range.
You cant just swag it. 134 is forgiving but only within a range of 1+or- for the chart.
A full charge at 75 is like 38/155.
Dont take my word for it. Here is a chart
 

KLXD

Top Post Dawg
Joined
Aug 22, 2009
Location
Lompoc, CA
TDI
'98, '2 Jettas
Nothing technical to add but I love the fogging glasses when you get out of the car. Reminds me of when I used to go to the Cape. Corners of the windshield would fog up on the outside.
 

AndyBees

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Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
No way. That's not even a valid range.
You cant just swag it.
If you notice my comment, I used the word "isn't" which means the comment is not poured in concrete and was just for the sake of discussion. Thanks for sharing the sticker with the accurate info.

Now, in my Vanagon with an ALH and the AC Compressor that come with the engine (and new hoses), there is no way of knowing the appropriate volume of 134a. But, I guarantee you, on 85f day, it will have "about" 45 PSI on the suction side and "something" over 200 PSI and will be cooling just fine. As suggested in other forums, for the Vanagon, I use a box fan to blow air on the grill while testing, adding refrigerant, etc., to supplement the air flow of the single fan.

As for Valid Range, 45 psi on the low-end is spot on at the temp I suggested (85f). I didn't use 75f in my comment.

Lastly, I'm pretty sure the 50g is 50g + or - (+ or -).
 

JimInPB

Active member
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Feb 3, 2019
Location
Florida
TDI
1999.5 ALH Jetta
Wow, that was a lot of responses & fast! Thanks guys. (y)

As for sub zero meaning a defective control valve, I agree with that. However, in places like AZ, I like to have that kind of defect. The Chinese valves are a roll of the dice. You never know what setting you will actually get. My luck of the draw on that one was too cold, which causes icing of the evap in humid conditions.

If you look at the pressure gauges on most AC sets, you will see different scales. One is temperature. My low side at 25psi was running below freezing at the port. I was not seeing that at the evap. That got me looking at the plumbing. What I found was condensation water just about pouring out the bottom of the car. This had been a slow drip in the past. That would explain where my extra cooling was disappearing to. Apparently, my insulation job from 5 years ago had some blow by. A little more investigation found what appears to be the root cause of my issue. A plastic bag had gotten sucked up into the air intake by the front passenger feet area inside the cabin. That had caused suction in the air handler, which forced some warm humid outside air to get sucked in. Removing humidity consumes a lot of cooling energy.

Just to test how much humid outside air would slug the system compared to recirculated cabin air, I switched to outside air & watched my high & low side pressures climb. They went to 48 & 340 psi. that's a lot. Ambient temperature was 91F at the time.

I removed the bag from the air handler intake & the airflow from the dash board immediately increased by about 4 fold. Also, the system pressures came down to 27/255psi. The air from the dash board came out at 38F. It appears that I may have permanently lost some of the insulation that I stuffed in there 5 years ago, since I'm not seeing sub freezing temperatures at the dash board anymore, but that's probably a good thing for Florida use. 38F from the dash board on a day when it's 92 degrees out is pretty good & I may not have the icing issue any more. It seems like I might have accidentally struck a workable balance between the over-cooling Chinese valve & loss of insulation that will be good enough for now.

I'll drive it around for a few days & see how it is.
 
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