Nominal A/C Refrigerant Pressure

[youthebest]

I'm not sure why my AC compressor doesn't kick in.
I filled the refrigerant with the tools I bought from autozone.
I checked the pressure by pressing "REST" button for 5 secs and then went to number 7.
It displayed 2*9 (* is degree sign).
I believe that number is in bar.
It used to be *2(almost like that) before I refilled it.

Is there a certain pressure that the compressor starts?
I think I also have seen that the number 8 would display refrig temp but mine stayed at 45 all the time.

Can someone also thell me what the number 15 displays?
It displayed "Lo", but I couldn't find what it represent in any forums.

[martattack]

I was about to post the EXACT same question yesterday actually, so hopefully someone can answer the A/C pressure question. Mine is at around 4 bar when the A/C is off


On the diagnostics, 15 represents the pre-selected interior temperature.

This PDF has the list and the procedure to get the codes:

http://202tech.mkosonen.com/misc/95actualvalues.pdf

[jnenad16]

yeah, you need at least 50-60psi( about 5 bar) of rest pressure for the compressor to kick on.

nenad

[martattack]

Originally posted by jnenad16
yeah, you need at least 50-60psi( about 5 bar) of rest pressure for the compressor to kick on.

nenad

nenad, do you know of a way to manually jump the compressor so I can add refridgerant? I know you can jump it with +12v to the terminal, but I know some cars have a way to do it via the a/c controls. Any ideas?

[youthebest]

Originally posted by jnenad16
yeah, you need at least 50-60psi( about 5 bar) of rest pressure for the compressor to kick on.

nenad
Thank you.
Yeah, that sounds about right.

I'm not sure if this is relevant but...
According to the Temp vs Pressure table for 134a, at about 85(today in Illinois) the pressure of the refrigerant should be almost 95psi(6.5bar). However, that pressure is relative to the sea level condition, so it will probably be lower than that. You can get this chart by searching "134a temperature pressure table".

I guess the pressure to recharge the ac system will vary depending on the temperature that day.

I'll give 5 bar a try.
Thank you for your help.

[jnenad16]

Originally posted by BoominBenz
nenad, do you know of a way to manually jump the compressor so I can add refridgerant? I know you can jump it with +12v to the terminal, but I know some cars have a way to do it via the a/c controls. Any ideas? you dont need to run the compressor to charge it, the system will take up to about 100 or so psi inoperable. do you have a good a/c manifold? you will need it to properly charge and diagnose the system operation. also, are you charging the freon as gas or liquid? it should be as liquid, that way you can inject enough freon for the compressor to kick on.

nenad

[youthebest]

I rechared the ac system upto 5.3~5.6 bar today.
The compressor started working at about 5bar.
But the air is still not cold.
I went into diag("REST" button) and verified that compressor was on(RPM changed).

So, the refrigerant has been recharged and compressor is working, what else could be wrong?

[1995c280]

Originally posted by youthebest
I rechared the ac system upto 5.3~5.6 bar today.
The compressor started working at about 5bar.
But the air is still not cold.
I went into diag("REST" button) and verified that compressor was on(RPM changed).

So, the refrigerant has been recharged and compressor is working, what else could be wrong?

i had enough freon, no leaks and compressor always turned on, but my a/c never blew out COLD air. found out it was the climate control unit that was faulty. even though all the functions on it works...somehow it was faulty and swapping for a new one fixed my problem. there was an a/c software update for the early w202's that the dealer should have done years ago. you might want to check on that!

Jason

[youthebest]

Originally posted by 1995c280
i had enough freon, no leaks and compressor always turned on, but my a/c never blew out COLD air. found out it was the climate control unit that was faulty. even though all the functions on it works...somehow it was faulty and swapping for a new one fixed my problem. there was an a/c software update for the early w202's that the dealer should have done years ago. you might want to check on that!

Jason

Yes I remember hearing that at the autozone or something.
If I remember this correctly, it was about if your diag display #9 as 03 then it should be updated.
Mine is 03. It said something about HTT update but I didn't know what HHT was.

Anyways, I'll check with a dealer here to get mine updated or somrthing.

[1995c280]

Originally posted by youthebest
Yes I remember hearing that at the autozone or something.
If I remember this correctly, it was about if your diag display #9 as 03 then it should be updated.
Mine is 03. It said something about HTT update but I didn't know what HHT was.

Anyways, I'll check with a dealer here to get mine updated or somrthing.

yeah that's is correct. it should flash as 03 so yours was updated. HHT means "hand held tester". it is the older version of SDS which is the computer that benz uses.

[jnenad16]

the only way the faulty control unit could keep the ac from getting cold is if the compressor was off and the pressure switch had an open circuit and the auxiliary fans would always be on. if that is the case, start with the switch, then move on to the control unit. if thats not the case, I would suggest you connect the a/c manifold to the service ports,and take a look at the pressure reading on the high side and the temp reading on the low side, if the high side is above 150psi and low side reading is always constant and below 30F, you are looking at a stuck closed expansion valve.

nenad

[1995c280]

thanks alot nenad. i'll check into that tomorrow when i'm at work.

Jason

[jnenad16]

Originally posted by 1995c280
thanks alot nenad. i'll check into that tomorrow when i'm at work.

Jason
you're welcome.:)

nenad

[youthebest]

Thanks alot.
I learned a lot of new stuff reading your replies in few forums.
I did the diag(REST and windshielf heat button) and found out that there is a continuous fault in Compressor Electromagnetic clutch(59).

I still don't know whether that fault is due to low freon.
You said something about 100psi at idle to get clutch working in another forum.
Is that right?
Mine read upto 6bar(87psi) today at 70degF.
Should I go ahead and give it a little more charge?

My current condition:
When I turn ac on, I see that freon's rushing inside hexagonal window under the hood right behind the left headlight.
When I change Engine RPM, compressor RPM also changes.
#7 is at 5.5-6 bar.
Checked all the fuses(OK)

[jnenad16]

Originally posted by youthebest
Thanks alot.
I learned a lot of new stuff reading your replies in few forums.
I did the diag(REST and windshielf heat button) and found out that there is a continuous fault in Compressor Electromagnetic clutch(59).

I still don't know whether that fault is due to low freon.
You said something about 100psi at idle to get clutch working in another forum.
Is that right?
Mine read upto 6bar(87psi) today at 70degF.
Should I go ahead and give it a little more charge?

My current condition:
When I turn ac on, I see that freon's rushing inside hexagonal window under the hood right behind the left headlight.
When I change Engine RPM, compressor RPM also changes.
#7 is at 5.5-6 bar.
Checked all the fuses(OK)
if you are getting the clutch code, Id assume the clutch electromagnet is getting weak and probably needs replacement. the rest pressure is fine. like I said earlier, its best to charge and diagnose the a/c system with a manifold. once its hooked up, then you can really see whats going on. I personally dont rely on the built in diagnostic in the control unit, I prefer to do everything manually. the window you refer to is the see through part of the filter/drier. another way to know if you have enough freon is to turn on the a/c and look at that glass part of the drier and if its cloudy, you are most likely low on freon, if its clear, than you have sufficient amount in the system.

nenad

[martattack]

Originally posted by jnenad16
if you are getting the clutch code, Id assume the clutch electromagnet is getting weak and probably needs replacement. the rest pressure is fine. like I said earlier, its best to charge and diagnose the a/c system with a manifold. once its hooked up, then you can really see whats going on. I personally dont rely on the built in diagnostic in the control unit, I prefer to do everything manually. the window you refer to is the see through part of the filter/drier. another way to know if you have enough freon is to turn on the a/c and look at that glass part of the drier and if its cloudy, you are most likely low on freon, if its clear, than you have sufficient amount in the system.

nenad

Is it possible to replace just the electromagnet?

[jnenad16]

no, the clutch needs to be changed as a whole.

nenad

[martattack]

Originally posted by jnenad16
no, the clutch needs to be changed as a whole.

nenad

I figured that, but can the clutch be replaced seperately from the compressor?

[jnenad16]

yes, it can.

nenad

[youthebest]

Originally posted by jnenad16
the only way the faulty control unit could keep the ac from getting cold is if the compressor was off and the pressure switch had an open circuit and the auxiliary fans would always be on. if that is the case, start with the switch, then move on to the control unit. if thats not the case, I would suggest you connect the a/c manifold to the service ports,and take a look at the pressure reading on the high side and the temp reading on the low side, if the high side is above 150psi and low side reading is always constant and below 30F, you are looking at a stuck closed expansion valve.

nenad

I want to check for a stuck closed expansion valve, how do I go about doing it. Only tools I have is the pressure gauge that has yellow, red, and blue hoses to check the pressure with just "low, full, alert..etc" displays.

How do I measure the low side temp?

Just in case you might find something, here's the list of "REST" diag.
01 - 87*F
02 - 73*F
03 - 88*F
05 - 83*F
06 - 16 9
07 - 5*8
08 - 28 0
09 - 03
15 - Lo
20 - 02
21 - 07*0
22 - 8*6
23 - 00*0
50 - 10*C
51 - 00
52 - 00

Are 05 and 06 sound about right?
I noticed that aux fan was not spinning at all even with my AC on.

[jnenad16]

I dont think I have ever run an ac self diagnostic, like I said I do everything manually. could you explain the figures in the chart?

nenad

[youthebest]

Originally posted by jnenad16
I dont think I have ever run an ac self diagnostic, like I said I do everything manually. could you explain the figures in the chart?

nenad

Ok.
01 In-car temp sensor 87degF
02 Outside Temp sensor 73degF
03 Heat excange temp sensor 88degF
05 Evaporator Temp sensor 83degF
06 Coolant Temp sensor (climate control) 169degC
07 Refrigerant Pressure 5.8 bar
08 Blower control voltage 2.8V
09 Software Status 03
15 Reselected interior Temp Lo
20 Variant code 02
21 Engine Speed 700RPM
22 A/C Compressor Speed 860RPM
23 Vehicle Speed 0Km/h
50 not assigned
51 Quantity of current slip recognitions (V-ribbed belt) 0
52 Quantity of stored slip recognitions (V-ribbed belt) 0

[martattack]

You evaporator temp sensor is reading extremely high, which is likely why you don't feel any cool air coming in. The temperature should be around 34-38ish degrees Farenheit with the compressor running. As far as where to start that diagnosis, I'm not sure.

[jnenad16]

thanx for clarifying that. now, to properly diagnose this, as I said before, you need to hook up a manifold and observe the gauges. the readings off of them can tell you a lot about the performance of your system. and looking at the values you provided, I agree with boominbenz that the evap sensor is reading quite high, but that just points a finger at a bad expansion valve. to determine this, do the following. turn the ac on, set it on lowest temp, wait a few minutes and touch the bare metal part of the low pressure line(one between compressor and the firewall/evap), and if its sweating and very cold and the vents are blowing warm air, the expansion valve is stuck closed and thats your problem. expansion valve usually goes bad if the ac is not used for a while or if you replaced something in the system which required emptying the system and not adding enough pag/ester oil when recharging.

nenad

[youthebest]

Originally posted by jnenad16
thanx for clarifying that. now, to properly diagnose this, as I said before, you need to hook up a manifold and observe the gauges. the readings off of them can tell you a lot about the performance of your system. and looking at the values you provided, I agree with boominbenz that the evap sensor is reading quite high, but that just points a finger at a bad expansion valve. to determine this, do the following. turn the ac on, set it on lowest temp, wait a few minutes and touch the bare metal part of the low pressure line(one between compressor and the firewall/evap), and if its sweating and very cold and the vents are blowing warm air, the expansion valve is stuck closed and thats your problem. expansion valve usually goes bad if the ac is not used for a while or if you replaced something in the system which required emptying the system and not adding enough pag/ester oil when recharging.

nenad


I tried to connect the manifold to the high and low pressure side, but I was unable to plug the red hose to the high side. It won't plug in. Aren't these plugs universal (it fits the low side)?
The low side pressure reads 60-65psi.

The high side is right behind the plastic cover for aux fans(at the left side of the fan). right?

Anywayz, I have an infrared temp sensor, but I didn't see any part that goes below 85degF today.


Is there some kind of trick involved or am I just not pushing the plug hard enough?

[jnenad16]

the low and high sides are different sizes. what kind of manifold are you using? it should look something like this:
http://www.yellowjacket.com/artwork/3028.jpg

now, are you saying that the low side line doesnt get cold? then the compressor is not working.

nenad

[youthebest]

Originally posted by jnenad16
the low and high sides are different sizes. what kind of manifold are you using? it should look something like this:
http://www.yellowjacket.com/artwork/3028.jpg

now, are you saying that the low side line doesnt get cold? then the compressor is not working.

nenad

I'll take some pictures and possibly some videos to show you what I got and video of my engine running.

[youthebest]

Hurray,
It's back in business.

While I was taking pictures, I realized what you said about the compressor not being operated.
You were right.

So I basically attached my manifold and checked the pressure.
I had to push quite hard to plug the high pressure side.
I found out that the high pressure was about 100psi.
So like you said, I held the refrigerant upside down to charge ir as liquid. The low pressure jumped up to about 60psi and then went down gradually to about 25-30 psi.
I used the whole can and ran to the auto store and got another can. I did the same thing. It went up gradually to about 45psi now. (From the diag screen #7 displays 12*8 which means 12.8bars. It doesn't make sense, so don't trust it) I started notice the difference.


1. Inside the hexagonal glass window, the liquid used to flow slowly, but now it's like flushing really fast and making bubbles.

2. Ticking sound started (like 2-3hz)

3. aux fan started spinning for 10secs and stopped and turned on again and again....

This point I realized tha my AC revived. ^_^

It's freezing now.

I wish I knew that I had to use more than 1 can (13oz) to fully charge my car.

Thank you all you guys.
From now, I will be able to help future victims of this newbie trouble.

Thanks especially to nenad

[jnenad16]

alright! Im glad I could help and save you some $$$. You are very welcome.

nenad