DubVBenz

I have a really weird AC issue that has proved impossible to troubleshoot...

The symptoms only occur in hot weather AND when the car is parked outside and allowed to bake in hot weather in the summer after a drive.

The sequence is:

1) Drive car for any amount of time with AC on in 85+ degree weather. Doesn't matter what level the blower is on or if recirc is being used
2) Park and turn off in said hot weather. Leave it parked anywhere between 1-75 Mins
3) Start the car up and resume AC

It manifests itself as the blower simply not turning on.. from anywhere from 60 seconds to 5-10 minutes. I know the compressor is on, because I can feel the cool ambient air floating out of the vents. When the blower decides to come on, i get a nice blast of the cold air the compressor has been creating for me.


The oddity: No fault codes. blower Regulator replaced. Obviously not a compressor problem since it's still engaged. It's like the head unit simply decides to not blow air.

Troubleshooting: Already stated that I replaced the blower regulator. I read that it could happen when using "Max AC" because the blower goes one step above the highest level in that scenario, however I never use "Max AC". I also don't put the fan at the highest manual level ever because of what I read during that research


Workaround: None really, I have tried powering off the entire HVAC system, I have tried playing with settings, etc. The only "fix" is to simply wait. After 2-15 minutes, eventually the blower comes on at whatever speed you've specified .


When does it occur: only when it's hot and I've parked after recently running. I've never had it happen on a cold start, it only happens after i restart after a trip. For example, if I drive to the grocery store, spend 20 minutes inside and then get back in the car, the blower may come back on for 5-10 minutes after i restart. This only happens when it's 80+ degrees out, never have I experienced a similar condition with the heating system in the winter.

PSDCampervan

I had this occur on mine but during extreme cold. I swapped out voltage regulator & blower fan with a salvage yard unit & everything has been working flawlessly since. Was replacement regulator you bought new or used? Perhaps it is as faulty as one that was replaced.

cmriv

maybe the blower motor itself is faulty. Or you could have a stepper motor issue. Only way to determine issue would be a voltmeter and some DAS actual values.
Can you state what vehicle you are driving.

DubVBenz

Sorry for the late replies..

Replacement regulator was brand new OEM. Car is a 2007 W211 E320 bluetec with the dual zone climate control.

Blower motor is the next step I guess, I was just hoping to avoid all of the labor involved, especially since the motor seems to blow just fine once it runs on.

Maroc_Specops

run ac diagnostics. Clear delete fault codes. 80% of the time it will fix it.

DubVBenz

Update:

Scanned with both Autologic and Star SDS, not a single code appeared. This was within 2 restarts and 45 minutes of the issue occurring...

I'm thinking I may as well throw a blower motor at it just to see if it resolves it, but it's odd that there are no codes.

cmriv

Erasing codes wont fix anything. Not sure how that will fix a mechanical issue.


You can DIY repair this actually except in the case of it being the a/c control unit itself which i highly doubt. You could r/r under panel and blower motor assembly. go to a benz dealer and purchase a new regulator (new parts are bad also) and a blower motor. Plug them in at the dealer and see what happens, now that you've diaged the issue purchase parts elsewhere for a cheaper price if that's your motive. Not a whole lot of labor involved until a/c system has new regulator and blower motor. if those are all new and refrigerant levels are adequate and within spec, at that point you'd need DAS and someone who know what is really going on....

GL

Ray_G

It is your control valve located in the compressor. I had the same issue. New valves are not available from the dealer, only aftermarket ones. The aftermarket ones work fine. The system has to be discharged when you take the valve out of the compressor or it goes boom.
https://www.polarbearinc.com/PBPC/ho...es.html#SD7V12

cmriv

If that valve was defective i couldn't see it causing a intermittent/inconstant issue like this.


Take the heat exchange switchover valve under the cowling as an example. It's mechanical and electronically controlled. When it's bad it's bad, there is no in between.

A bad valve in the compressor isn't going to prevent the blower motor from coming on. Even if you have low refrigerant in the system the blower motor should till turn on.... If your compressor is shot, your blower motor should still turn on.


people that remove ac from their vehicles should still have blower motor actuation.....


control unit, blower motor or regulator are the issue. Air conditioning is irrelevant UNLESS this issue only occurs when the a/c button/feature is actuated.


OP have you tried to cut blower on without actuating ac??????

DubVBenz

Thank you for the input. Yes, I have tried turning off the compressor with the head unit switch. I've also tried powering off the whole thing using the "off" button, switching from recirc back to non recirc, changing fan speeds and trying max-cool. When this issue cropped up (very sporadically) a couple of years ago, some forum members mentioned an overvoltage condition that could occur under max cool or when the blower was at full speed. I stopped using both, but the condition persists. At that time, I replaced the regulator with a brand new OEM regulator, which did not fix it.

When the issue happened yesterday, I hooked up an autologic and monitored the real-time values of the AC system. Even at max cool did nothing exceed (or even approach) the tolerable upper limits.

Just such an odd behavior. Like I said, I'll be throwing a blower motor at it next week to see if it fixes it. Compressor is perfect, no leaks and the air temp is cold when i can measure it. I check for leaks every summer and it barely ever falls. Compressor is also variable and you can tell that it's cycling on and off when you turn the AC on or off at the AC unit, simply because of the engine RPM adjustment (diesel bluetec here).

cmriv

To me it sounds like a bad new shorted regulator. You have a warranty on it for 12 months so if i were you i'd return it as defective and ask for a replacement one just to be safe. keep us posted.


What is your refrigerant level???? When is the last time the a/c system has been evacuated, put into a vacuum and filled?

DubVBenz

Car is in the shop this week to replace the blower (along with oil cooler seal, preventative only). System is fully charged as of a month or two ago, the process of charging does the full evacuation as part of the process. I still have the old regulator, so if the issue persists I'll put it back in before turning my attention to the head unit.

DubVBenz

Update: New blower motor has solved the issue. No signs of damage on the old motor and it spins freely, so not sure what was wrong, but the symptoms went away with the new one.