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HVAC Actuators

3K views 7 replies 2 participants last post by  TucE320 
#1 ·
There are a number of threads about actuators but I couldn't find the specific function of some of them. What is the specific function of the right and left center outlet tempering flap actuators (#42 & #43)? What is the effect of them being closed vs. being open (i.e. when vacuum applied and when vacuum not applied to the actuators)? Thanks for your help.
 
#3 ·
So to be clear (with car idling, AC on):
1. If there is a vacuum to #42, the right center outlet tempering flap, warm air should pass through the passenger (U.S.) side of the center vent.
2. If there is no vacuum to #42, cool air should pass through the passenger (U.S.) side of the center vent.
1. If there is a vacuum to #43, the left center outlet tempering flap, warm air should pass through the driver side of the center vent.
2. If there is no vacuum to #43, cool air should pass through the right side of the center vent.

Thanks for your quick response.
 
#4 ·
If you followed the flap test sequence, yes. Here is the airflow diagram for W220 which is similar to W210. W220 has electric actuators for the flaps, W210 has vacuum actuators. Tempering is mostly used in AUTO operation (by opening and closing these flaps as needed to keep the temps close the set values).

What seems to be the problem?
2625749
 
#5 ·
Thanks for the help. This is the same problem from the end of last summer (thread “AC Fan Speed Starts/Stops”) that you, and others, helped me address. I thought I would try again as summer is approaching. The issue is that the AC air flow from the center vents works great at idle but is greatly diminished with increased engine load, thought to result from the lower manifold vacuum. As a summary from last summer, after testing the individual vacuum lines directly at the switchover valve (Y11), the right center outlet tempering flap vacuum actuator (#4 port on Y11), the left center outlet tempering flap vacuum actuator (#3 port on Y11), and the left defrost flap actuator (#5 port on Y11) all do not hold vacuum. Also, the SRU port on the PSE does not hold a vacuum if tested directly at PSE port. The check valve between cabin and reservoir is functional. I recently replaced the blower fan and resistor with the updated versions of these but experienced same problem. I also recently serviced the AC at professional shop that removed all refrigerant and replaced with correct weight (950 grams) resulting in very cold air coming from AC.
I will go back and run through the tests that you, and others, suggested and get back to the forum with observations. The question in this thread was to confirm that the tempering flaps are open when no vacuum is applied, therefore no vacuum loss from these in manual AC mode, LO temperature setting. The only actuator leak would therefore be at the defrost flap actuator (#5 port on Y11). This and any other leaks are overcome by the higher vacuum at idle. I will again follow your suggestions to test in REST mode but if earlier observations repeat (i.e., the very low vacuum observed in REST mode), I think I will first cap the #5 port and/or address the PSE and observe. I’ll keep all posted.
 
#6 ·
Hopefully this issue is resolved, not perfectly but completely adequate. I exposed the HVAC vacuum manifold (Y11) and tested various conditions as described below.
  • With components in initial state. Problem not resolved.
  • As stated in prior post, I previously determined the actuators that were leaking vacuum.
  • I capped lines for the right center outlet tempering flap vacuum actuator (#4 port on Y11), the left center outlet tempering flap vacuum actuator (#3 port on Y11), the left defrost flap actuator front port (#5 port on Y11), and the left defrost flap actuator back port (#6 port on Y11). Problem not resolved.
  • Left lines capped as in #2 above and capped SRU line in the PSE (both the line and the SRU outlet on the PSE). PSE pump ran short time and problem resolved.
  • The PSE SRU port does not hold a vacuum and is thus an “open” vent for the vacuum system. I decided to try to leave as many flap actuator lines connected to the flaps as possible, even though I know they leak.
  • I left all of lines connected to the actuators except for capping the left defrost flap actuator back port (#6 port on Y11), problem not resolved.
  • I left the right center outlet tempering flap vacuum actuator (#4 port on Y11) and the left defrost flap actuator front port (#5 port on Y11) connected to the actuators and capped the left center outlet tempering flap vacuum actuator (#3 port on Y11) in addition to the previously capped left defrost flap actuator back port (#6 port on Y11). Problem resolved.
  • In the end, the two lines (the left center outlet tempering flap vacuum actuator (#3 port on Y11) and the left defrost flap actuator back port (#6 port on Y11) were capped, the SRU port and line were capped, and everything else connected.
  • With the various vent settings, cold air is coming from center, floor, side vents, and defrost vents without lag of air volume when the vacuum is diminished when engine is under a load.
  • I recognize that the REST function will not work, not a problem for me.
  • I am not sure what effect this will have on the AUTO mode. If it doesn’t work well, again, not a problem for me compared to the way it was.
  • Overall a low cost ($0.00) work-around for a major operational problem where the appropriate repair is such an issue with the difficult dash removal and with the potential for broken, plastic parts that are difficult to impossible to acquire.
  • Comments/questions more than welcome.
 
#7 ·
I would test the defroster function to make sure it has enough airflow as you capped the back port of the left actuator. The defroster actuator works on two strokes short and long+short. I do not remember but I think that the short stroke was 20 percent (leak) and the long stroke provides additional 80 percent. So if the defrost does not have enough airflow it may not remove the frost under certain conditions. You can check that out in the defrost mode. Else, some cloth and a long arm will do :).
 
#8 ·
Thanks. That is a good suggestion. I was concerned with this but the port that is still active is nearest the vacuum line and supports the long stroke. It will leak through the other port but hopefully, in full defrost mode, it will have enough vacuum to be acceptable. In testing there is still a good airflow from the upper vent. Also, fortunately where I live, I don't experience heavy windshield frost conditions so hopefully it will be fine. In the very worst case, and I wanted to fix it, that actuator is accessible (with great effort) with the removal of the instrument cluster. However, the connector to the plastic flap is very brittle and if broken, you are truly screwed. The connector is removable at the actuator so possible, but not a pleasant job.
 
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