A/C diagnostics instructions & analysis utility
Thread Starter
Super Member
Joined: Nov 2004
Posts: 588
Likes: 1
'98 E320 4Matic, '85 380SL
A/C diagnostics instructions & analysis utility
It's that time of year when many discover that their air conditioner didn't make it through the winter.
I wrote instructions for grabbing climate control sensor values and error codes and -- this is the new twist -- a small utility that analyzes the numbers & codes to figure out what's wrong.
The analysis is by no means comprehensive, but it can diagnose 4 or 5 common A/C problems. I've tried my best to make it accurate. I fed it sensor values that people had posted in the archives and checked that the answer given matched the final resolution of their problem.
Take a look! Try it with your numbers. Let me know if you spot any bugs.
I wrote instructions for grabbing climate control sensor values and error codes and -- this is the new twist -- a small utility that analyzes the numbers & codes to figure out what's wrong.
The analysis is by no means comprehensive, but it can diagnose 4 or 5 common A/C problems. I've tried my best to make it accurate. I fed it sensor values that people had posted in the archives and checked that the answer given matched the final resolution of their problem.
Take a look! Try it with your numbers. Let me know if you spot any bugs.
Last edited by lexrex; May 22, 2006 at 10:35 AM.
Member
Joined: Sep 2003
Posts: 108
Likes: 0
From: St. Louis, Mo
1999 E55
Thanks.
In your error code instructions you say -
"Decrease the left side temperature (right cold arrow) until right side says “LO.” " It should say right side temp. I tried it a few times before I read inside the parenthesis.
In your error code instructions you say -
"Decrease the left side temperature (right cold arrow) until right side says “LO.” " It should say right side temp. I tried it a few times before I read inside the parenthesis.
Member
Joined: Sep 2003
Posts: 108
Likes: 0
From: St. Louis, Mo
1999 E55
Here is a link to another thread describing the location of the evap sensor.
https://mbworld.org/forums/showthrea...041#post163904
Between Lexrex and mikejosh I managed to save a trip to the dealership, and a few dollars. I am not sending either of you any money but if you lived nearby I would buy drinks.
https://mbworld.org/forums/showthrea...041#post163904
Between Lexrex and mikejosh I managed to save a trip to the dealership, and a few dollars. I am not sending either of you any money but if you lived nearby I would buy drinks.
Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
That's very cool website.
But....... I have a very weird problem.
I had my air condition charged today.
Tech advice me to drive at least 15 min w/ Fan on FULL Blast, set both side to "LO" on my climate control.
Here is the problem, while both set to "LO", passenger-side blowing FREEZING COLD air, but driver-side are blowing just COLD air.
I am sure there are at least few degrees different between them.
Why is that happening? I am sure my air condition system are in great shape, both are blowing nice cold air, but I like to have my driver side blowing artic chill.
Is there an adjustment or thing need to be replaced? ( Both set to "Lo" )
thanks,
But....... I have a very weird problem.
I had my air condition charged today.
Tech advice me to drive at least 15 min w/ Fan on FULL Blast, set both side to "LO" on my climate control.
Here is the problem, while both set to "LO", passenger-side blowing FREEZING COLD air, but driver-side are blowing just COLD air.
I am sure there are at least few degrees different between them.
Why is that happening? I am sure my air condition system are in great shape, both are blowing nice cold air, but I like to have my driver side blowing artic chill.
Is there an adjustment or thing need to be replaced? ( Both set to "Lo" )
thanks,
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Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
Originally Posted by raymond g-
do you have figures from the diag prior to A/C service?
run the diag again now and post before and after figures
run the diag again now and post before and after figures
What is the "possible" cause?
Last edited by no_clue; Jul 21, 2006 at 01:33 AM.
MBWorld Fanatic!
Joined: Jan 2004
Posts: 5,939
Likes: 178
From: Seattle WA
99 E320
will defer to lexrex et al, who have more hands-on, but my first guess is low
refrig....notwithstanding that you believe it is in good health.
so we need to second guess everything. the diag figures are important.
otherwise we end up trying to herd cats. i kind of ruled out duovalve because i
didn't think sticking would result in cold/colder...usually hot/cold. hmmmm
refrig....notwithstanding that you believe it is in good health.
so we need to second guess everything. the diag figures are important.
otherwise we end up trying to herd cats. i kind of ruled out duovalve because i
didn't think sticking would result in cold/colder...usually hot/cold. hmmmm
Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
Originally Posted by raymond g-
will defer to lexrex et al, who have more hands-on, but my first guess is low
refrig....notwithstanding that you believe it is in good health.
so we need to second guess everything. the diag figures are important.
otherwise we end up trying to herd cats. i kind of ruled out duovalve because i
didn't think sticking would result in cold/colder...usually hot/cold. hmmmm
refrig....notwithstanding that you believe it is in good health.
so we need to second guess everything. the diag figures are important.
otherwise we end up trying to herd cats. i kind of ruled out duovalve because i
didn't think sticking would result in cold/colder...usually hot/cold. hmmmm
Seems so complicate, as one side would go FREEZing and one side would go COLD only. (aren't both side come from same compressor? )
MBWorld Fanatic!
Joined: Jan 2004
Posts: 5,939
Likes: 178
From: Seattle WA
99 E320
yes...but you have dual climate control car, right? 
if you didn't, then would
be even more of a mystery. so we need to break it down to the actual components
of this system and figure out why dissimilar temp under same settings for each
side. is there a door not fully closed and letting outside air mix in with AC air
on your side? i dont have enough smarts to answer this one yet.
so, as soon as you can i'd run the diagnostic and report back the figures.
dont know if night time will provide a good indicator....prob more when AC
is under load.
if you didn't, then wouldbe even more of a mystery. so we need to break it down to the actual components
of this system and figure out why dissimilar temp under same settings for each
side. is there a door not fully closed and letting outside air mix in with AC air
on your side? i dont have enough smarts to answer this one yet.
so, as soon as you can i'd run the diagnostic and report back the figures.
dont know if night time will provide a good indicator....prob more when AC
is under load.
Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
Originally Posted by raymond g-
yes...but you have dual climate control car, right? if you didn't, then would
be even more of a mystery. so we need to break it down to the actual components
of this system and figure out why dissimilar temp under same settings for each
side. is there a door not fully closed and letting outside air mix in with AC air
on your side? i dont have enough smarts to answer this one yet.
so, as soon as you can i'd run the diagnostic and report back the figures.
dont know if night time will provide a good indicator....prob more when AC
is under load.
if you didn't, then wouldbe even more of a mystery. so we need to break it down to the actual components
of this system and figure out why dissimilar temp under same settings for each
side. is there a door not fully closed and letting outside air mix in with AC air
on your side? i dont have enough smarts to answer this one yet.
so, as soon as you can i'd run the diagnostic and report back the figures.
dont know if night time will provide a good indicator....prob more when AC
is under load.
Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
OKAY....no error code at all.
(after 5 min of running)
1:30
2:36
3:24
4:21
5:19
6:54
7:15
8:59
E: FF
so.........why why why? Why I have one side colder than the other?
(after 5 min of running)
1:30
2:36
3:24
4:21
5:19
6:54
7:15
8:59
E: FF
so.........why why why? Why I have one side colder than the other?
Thread Starter
Super Member
Joined: Nov 2004
Posts: 588
Likes: 1
'98 E320 4Matic, '85 380SL
Here's the deal. Although the car has dual climate control, both sides share a single evaporator. Warm air blows over the evaporator on each side. Blowing warm air over the evaporator cools the air and heats the refrigerant inside. Think of dropping ice cubes in a glass of warm water -- the ice warms up (melts) and the water gets colder.
After passing through the evaporator, the cold air is then blended with ambient/warm air flowing through the heater core on each side to arrive at the appropriate dual zone temperatures.
The direction of refrigerant flow through the evaporator is right to left. This means that the refrigerant cools the passenger air first before it makes it way over to the driver's side. The evaporator is almost always warmer on the driver side than the passenger side. If your fan speed is near the top, you'll get a noticeable difference right & left. This is normal due to the design of the system and is even more pronounced when you're low on refrigerant.
I suggest that you close the passenger side vent, which will force all the air out the left vent and center vents. Point them both at you. As I said, this can also be caused by low refrigerant, so you might want to try getting your system recharged. Your pressure (#7 = 15) looks fine if in units of Bar, but way too low if PSI.
After passing through the evaporator, the cold air is then blended with ambient/warm air flowing through the heater core on each side to arrive at the appropriate dual zone temperatures.
The direction of refrigerant flow through the evaporator is right to left. This means that the refrigerant cools the passenger air first before it makes it way over to the driver's side. The evaporator is almost always warmer on the driver side than the passenger side. If your fan speed is near the top, you'll get a noticeable difference right & left. This is normal due to the design of the system and is even more pronounced when you're low on refrigerant.
I suggest that you close the passenger side vent, which will force all the air out the left vent and center vents. Point them both at you. As I said, this can also be caused by low refrigerant, so you might want to try getting your system recharged. Your pressure (#7 = 15) looks fine if in units of Bar, but way too low if PSI.
Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
Originally Posted by lexrex
Here's the deal. Although the car has dual climate control, both sides share a single evaporator. Warm air blows over the evaporator on each side. Blowing warm air over the evaporator cools the air and heats the refrigerant inside. Think of dropping ice cubes in a glass of warm water -- the ice warms up (melts) and the water gets colder.
After passing through the evaporator, the cold air is then blended with ambient/warm air flowing through the heater core on each side to arrive at the appropriate dual zone temperatures.
The direction of refrigerant flow through the evaporator is right to left. This means that the refrigerant cools the passenger air first before it makes it way over to the driver's side. The evaporator is almost always warmer on the driver side than the passenger side. If your fan speed is near the top, you'll get a noticeable difference right & left. This is normal due to the design of the system and is even more pronounced when you're low on refrigerant.
I suggest that you close the passenger side vent, which will force all the air out the left vent and center vents. Point them both at you. As I said, this can also be caused by low refrigerant, so you might want to try getting your system recharged. Your pressure (#7 = 15) looks fine if in units of Bar, but way too low if PSI.
After passing through the evaporator, the cold air is then blended with ambient/warm air flowing through the heater core on each side to arrive at the appropriate dual zone temperatures.
The direction of refrigerant flow through the evaporator is right to left. This means that the refrigerant cools the passenger air first before it makes it way over to the driver's side. The evaporator is almost always warmer on the driver side than the passenger side. If your fan speed is near the top, you'll get a noticeable difference right & left. This is normal due to the design of the system and is even more pronounced when you're low on refrigerant.
I suggest that you close the passenger side vent, which will force all the air out the left vent and center vents. Point them both at you. As I said, this can also be caused by low refrigerant, so you might want to try getting your system recharged. Your pressure (#7 = 15) looks fine if in units of Bar, but way too low if PSI.
Thanks for your explaination. I got the #7:15 off the diag code from the climate control. I think my refrigerant should be okay. I just had it charged yesterday and it is indeed blowing FREEZING air (only passenger side).
This afternoon, I also cleaned the Duovalve. (just in case)
It is kind of funny that my gf always complain it is too cold while I am just comfortable. (both set at 70F, hmmm....does man suffer hot-flash when hitting mid-life crisis?
)P.S. is it true I should have my old R134a drain out / flash out every 2 years before add new batch of R134a?????????????? (it cost extra $40, but I was wondering if that's truth or total BS? I meant, my kitchen freezer been operating for 8 years, and never change anything. Why do I need to flash my car's R134a??????)
Last edited by no_clue; Jul 21, 2006 at 06:13 PM.
Thread Starter
Super Member
Joined: Nov 2004
Posts: 588
Likes: 1
'98 E320 4Matic, '85 380SL
P.S. is it true I should have my old R134a drain out / flash out every 2 years before add new batch of R134a?????????????? (it cost extra $40, but I was wondering if that's truth or total BS? I meant, my kitchen freezer been operating for 8 years, and never change anything. Why do I need to flash my car's R134a??????)
I'm not sure what you mean about it costing an extra $40. To properly recharge, they must discharge the system completely anyways. The system holds 1 kg of refrigerant, and they have no way of knowing how much R134a is in there (and hence how much to add in a recharge) without evacuating and measuring.
Super Member
Joined: Mar 2006
Posts: 606
Likes: 4
From: Bellevue, WA
.... nothing to brag about, it is a previous model....
Originally Posted by lexrex
No. It's a sealed system. No need to "drain / flush" ever.
I'm not sure what you mean about it costing an extra $40. To properly recharge, they must discharge the system completely anyways. The system holds 1 kg of refrigerant, and they have no way of knowing how much R134a is in there (and hence how much to add in a recharge) without evacuating and measuring.
I'm not sure what you mean about it costing an extra $40. To properly recharge, they must discharge the system completely anyways. The system holds 1 kg of refrigerant, and they have no way of knowing how much R134a is in there (and hence how much to add in a recharge) without evacuating and measuring.
Super Member
Joined: Jul 2003
Posts: 693
Likes: 1
From: Mansfield, TX
11 ML350W2 / 17 GLC300
Lexrex,
Thanks for the utility. I inputed the numbers and your utility suggested that the AC was working well but the duovalve may be faulty. I found another web site that described cleaning the duovalve along with pictures of the valve and the inside parts. I cleaned the duovalve and now I can store meat in my wagon. I drove it to the office the other day and the evap temp was 33 f and the heater core temps at 35 f. Thanks again for your fine work.
Jim
Thanks for the utility. I inputed the numbers and your utility suggested that the AC was working well but the duovalve may be faulty. I found another web site that described cleaning the duovalve along with pictures of the valve and the inside parts. I cleaned the duovalve and now I can store meat in my wagon. I drove it to the office the other day and the evap temp was 33 f and the heater core temps at 35 f. Thanks again for your fine work.
Jim
MBWorld Fanatic!
Joined: Jan 2004
Posts: 5,939
Likes: 178
From: Seattle WA
99 E320
tip: before you pull the top off the duovalve, pack half dozen sheets of
paper towels around/below the valve. approx 1 oz of stuff will spill out,
down the fender, onto the floor.....and the dog will come up, "hey, wuz
diss?" and try licking some of it.
it will also help to catch any moving/loose parts that might fall
removing the torx fasteners is easy. a little trickier placing them back on
given the low clearance. you need fingers like ET.
consider using blue masking tape...punch the screw through....and dangling
the fastener above the hole before tightening. just before final twist, rip
the tape free from the screw.
paper towels around/below the valve. approx 1 oz of stuff will spill out,
down the fender, onto the floor.....and the dog will come up, "hey, wuz
diss?" and try licking some of it.
it will also help to catch any moving/loose parts that might fall
removing the torx fasteners is easy. a little trickier placing them back on
given the low clearance. you need fingers like ET.
consider using blue masking tape...punch the screw through....and dangling
the fastener above the hole before tightening. just before final twist, rip
the tape free from the screw.
Super Member
Joined: Jul 2003
Posts: 693
Likes: 1
From: Mansfield, TX
11 ML350W2 / 17 GLC300
This is the site that described disassembling and cleaning the duovalve: http://www.benzworld.org/forums/w210...-cold-air.html
Member
Joined: May 2006
Posts: 197
Likes: 0
1997 E320
lexrex,
What is the optimal range for sensor #7, the refrigerant pressure? I used your diagnostic tool and I punched in 25 for #7 and it told me that it's low. Looking at the chart I see the reading from #7 ranges from 10 to 15 so is my system overcharged or low on refrigerant? If it is overcharged how can I drain the extra? I'm guessing I'll just stick a pin in the low pressure port and let it out? thanks
one more thing, I do hear a hissing noise sometimes from the vents, which you said is a sign of low refrigerant.
What is the optimal range for sensor #7, the refrigerant pressure? I used your diagnostic tool and I punched in 25 for #7 and it told me that it's low. Looking at the chart I see the reading from #7 ranges from 10 to 15 so is my system overcharged or low on refrigerant? If it is overcharged how can I drain the extra? I'm guessing I'll just stick a pin in the low pressure port and let it out? thanks
one more thing, I do hear a hissing noise sometimes from the vents, which you said is a sign of low refrigerant.
Last edited by koskesh; Jul 24, 2006 at 05:18 PM.
