A/C problem - one side hot other side cold
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Joined: Jul 2005
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E420 '97 , e320 '98
A/C problem - one side hot other side cold
Hi. I had issues before that the AC stared to blow warm air and was fixed by adjusting the temperature but yesterday after driving for 40 minutes I made a short stop. After starting the car I noticed the left vent was blowing hot air and center and right vent blew cold. I could not remedy the problem by lowering both side temp control to LOW. Drove to work and parked. last night everything was fine on the way home. Today the same problem, after the short stop. I would appreciate any help. Car is E420 1997.
here is the diag readout from the AC display
1 -24 in car temp
2- 36 outside temp
3-74 heater core temp left side
4- 24 heater core temp right side
5- 02 evap temp sens
6- 93
7- 11 ref. pressure
40 - 71
41- 34
Regards
Amir
here is the diag readout from the AC display
1 -24 in car temp
2- 36 outside temp
3-74 heater core temp left side
4- 24 heater core temp right side
5- 02 evap temp sens
6- 93
7- 11 ref. pressure
40 - 71
41- 34
Regards
Amir
Last edited by AmirB; Jul 28, 2005 at 10:43 AM.
Super Member
Joined: Nov 2004
Posts: 588
Likes: 1
'98 E320 4Matic, '85 380SL
Your evaporator temps & pressures look about normal. 
It looks like your heater duovalve is sticking on the left side. Notice that your left side heater core (#3) is considerably warmer than the outside air (#2). Low refrigerant pressure can cause the left side to blow warmer air than the right side (#4), but in no case will low pressure cause the air on one side to be warmer than the outside air. Your problem is that the left side heater is stuck on.
The duovalve controls how much hot engine coolant circulates through the left & right heater cores. If it sticks open on one side, it'll heat the air passing on that side. I would expect cold air to blow out of both sides and warm gradually out of the left as the engine warms up.
Sometimes tapping the valve with a screwdriver loosens it up. If it sticks regularly, you'll need a new valve. If you don't feel like fixing it, close the vent on the left side by the door. If your diverter flaps are working properly, the left-center vent should blow cold air without passing through the heater. Good luck!
The duovalve hasn't been discussed on this forum, but the folks on BenzWorld have talked about it. Here is some additional reading material from the BenzWorld forum:
It looks like your heater duovalve is sticking on the left side. Notice that your left side heater core (#3) is considerably warmer than the outside air (#2). Low refrigerant pressure can cause the left side to blow warmer air than the right side (#4), but in no case will low pressure cause the air on one side to be warmer than the outside air. Your problem is that the left side heater is stuck on.The duovalve controls how much hot engine coolant circulates through the left & right heater cores. If it sticks open on one side, it'll heat the air passing on that side. I would expect cold air to blow out of both sides and warm gradually out of the left as the engine warms up.
Sometimes tapping the valve with a screwdriver loosens it up. If it sticks regularly, you'll need a new valve. If you don't feel like fixing it, close the vent on the left side by the door. If your diverter flaps are working properly, the left-center vent should blow cold air without passing through the heater. Good luck!
The duovalve hasn't been discussed on this forum, but the folks on BenzWorld have talked about it. Here is some additional reading material from the BenzWorld forum:
Last edited by lexrex; Jul 28, 2005 at 11:23 AM.
Thread Starter
Newbie
Joined: Jul 2005
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E420 '97 , e320 '98
Thank you Blake. I will try to find the duovalve and follow the instruction of lubricating them. I should run the flap test too! When you say the right side of the car is that the passenger side?
Regards
Amir
Regards
Amir
Newbie
Joined: May 2012
Posts: 1
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From: Kaduna, Nigeria
2003 E320 Mercedes benz
I own an E320, 2003 model with similar a/c cooling problem like the one mentioned above (i.e cooling from the passenger side while blow hot air from the driver side's two vents). But mine seems to loose its coolant suddenly after about 3 to 4 days. Checks by a/c attendant revealed no leakages! I can understand valves malfunctioning but where does the coolant always leak into? I also notice a small rapture on the outside hot air hose linking the engine cooling system but the a/c man keeps telling me it has nothing to do with the loss of the coolant. What do you think is really the problem?
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