AC Question. Still HOT in Houston. Need expert opinion! - Page 2 - PeachParts Mercedes-Benz Forum

scoodidabop · #16 08-07-2009, 12:07 AM

Quote:

Originally Posted by kingdoc1

Has any repairs been done on the system recently where some moisture could have entered?

What you describe could be a symptom of moisture freezing in the expansion valve.

I do not know. I just bought the car. Sounds like a strong possibility though.

scoodidabop · #17 08-07-2009, 12:14 AM

Quote:

Originally Posted by whunter

Bypass the heater core or Pinch off the heater hoses for this testing, if the vent temperature suddenly drops = a bad mono valve..

What is the operating system pressure (engine running)?
What is the static (engine off) system pressure?

If the system pressure is correct.
Educated Guess:

Evaporator temperature sensor (two male spade connectors)
MB# 003 820 24 10

This sensor commands compressor cycling to prevent evaporator core freeze up/ice.
When the Evaporator temperature sensor fails CLOSED = the compressor will NOT cycle = the evaporator core becomes a block of ice = no cold air flow.

#1. Remove the glove box pocket.
#2. Disconnect one of the two male spade connectors.
#3. Start engine.
#4. The compressor should now be off.
#5. Use an infrared thermometer on the evaporator vapor line (return = large) to get a temperature base reading (write down the temp).
#6. Connect the wire you removed for one minute, and repeat step #5 (write down the temp).
#7. Wait one minute, repeat step #6 for two minutes, and repeat step #5 (write down the temp).
#8. Wait one minute, repeat step #6 for three minutes, and repeat step #5 (write down the temp).
#9. Wait one minute, repeat step #6 for four minutes, and repeat step #5 (write down the temp).
#7. Wait one minute, repeat step #6 for five minutes, and repeat step #5 (write down the temp).
Etc, etc,etc, up to fifteen minutes, if the evaporator temperature sensor is working, the compressor should cycle several times, and the output line temperature will stabilize somewhere above 36 F.

Have a great day

Verified the mono-valve is working just fine.

How often would the compressor cycle on/off? I haven't observed it for a sustained period of time to note if it's cycling. I will try this asap. Can't test it now; I'm installing my new Monark nozzles! Hopefully I can get to it by the weekend, although I am battling a rather large stack of kids laundry that needs attention. My wife doesn't fully understand my obsession, so I'm forced to help with the laundry. I guess it's not enough that I vacuum, clean rooms, and remodel things obsessively. Oh well.

Thanks a lot for the help on this one guys. Once again your knowledge seems bottomless. I really appreciate it.

I'll update after the old beast is breathing again... the car... not my wife

#18 08-07-2009, 06:59 AM

Have you checked the foam hose at the dash sensor yet?

scoodidabop · #19 08-07-2009, 08:08 AM

Quote:

Originally Posted by LarryBible

Have you checked the foam hose at the dash sensor yet?

No I have not. Wouldn't this only effect performance if I was using the "automatic" blower setting?

Brian Carlton · #20 08-07-2009, 09:41 AM

Quote:

Originally Posted by scoodidabop

Verified the mono-valve is working just fine.

How often would the compressor cycle on/off? I haven't observed it for a sustained period of time to note if it's cycling. I will try this asap. Can't test it now; I'm installing my new Monark nozzles! Hopefully I can get to it by the weekend, although I am battling a rather large stack of kids laundry that needs attention. My wife doesn't fully understand my obsession, so I'm forced to help with the laundry. I guess it's not enough that I vacuum, clean rooms, and remodel things obsessively. Oh well.

You've got two situations:

1) The compressor is not cycling.

This is a non-issue at this point. The system needs to get fully cold with the evaporator down to the setpoint temperature before the compressor will cycle. This can only occur after at least 10 minutes of steady running and could be quite a bit longer if the ambient is high. Some folks have the compressor running at 100% duty cycle to keep up with the heat load.

2) The system starts to produce cold refrigerant and then suddenly stops after a few minutes, although the compressor continues to rotate.

This issue needs to be addressed now. I would suggest that you'd need a set of gauges to watch while this shutdown of the system occurs. With some readings, the fellows who do this on a daily basis can provide some guidance.

#21 08-07-2009, 09:56 AM

It only takes about fifteen minutes to check the foam tube.

scoodidabop · #22 08-08-2009, 01:09 AM

I pulled all the injectors, then did a valve adjustment. Then I removed the Lovecraft system (!!) from under the hood. After I finish installing the new nozzles in the injectors I'll fire up the car again and try to supply additional diagnostics...

#23 08-08-2009, 05:09 AM

Have you checked the foam tube that connects the temp sensor below the small square grill in the center of the dash to the pipe behind the glove box?

scoodidabop · #24 08-10-2009, 01:59 AM

Quote:

Originally Posted by LarryBible

Have you checked the foam tube that connects the temp sensor below the small square grill in the center of the dash to the pipe behind the glove box?

I just bought a dash from a forum member. Looks like I'll be getting up close and personal with that tube really soon.

3 injectors installed... 2 left.... I'll probably finish tomorrow.... laundry has made NO progress!! Doh!

scoodidabop · #25 08-12-2009, 09:49 AM

UPDATE!!

Well I finished my injectors (see new thread for new issue!!)

I now notice that when I run the compressor, it makes a noise like a half dozen marbles slowly rolling around in a cardboard box. I have no idea what this indicates.... Might I need to install a new compressor and start from scratch? I would really like to avoid that, but it could be.... (Agent Smith's voice)... inevitable....

scoodidabop · #26 08-12-2009, 10:06 AM

Oh, to Larry...

The dash will be coming out before Friday, so I'll check that tube and replace if I need to asap....

tangofox007 · #27 08-12-2009, 10:19 AM

Quote:

Originally Posted by scoodidabop

I now notice that when I run the compressor, it makes a noise like a half dozen marbles slowly rolling around in a cardboard box. I have no idea what this indicates....

It indicates a loose drive belt.

rrgrassi · #28 08-12-2009, 10:27 AM

Quote:

Originally Posted by tangofox007

It indicates a loose drive belt.

Yep, check the drive belt tension.

Also, if it does that same noise, and the belt is correctly tensioned, it could be a failing clutch assembly bearing. That is what happened to me. It got to where it was noisy no matter what, so I had to cut the belt, until I installed a NEW compressor.

#29 08-12-2009, 01:57 PM

With the engine off and no one inside the car, turn the front portion of the compressor by hand. With the clutch not engaged, this is turning the internals of the compressor only. It should feel very smooth, only feeling the compression pulses. If it is smooth, remove the belt and give the pulley portion of the clutch a spin to make sure it's smooth. If so, then inspect, reinstall and properly tension the belt.

Cervan · #30 08-12-2009, 04:55 PM

the system is simply undercharged.. since the thermostat isnt reaching its desired temperature because their isnt enough freon in the system to cool the evap to that point. thats why your compressor is staying on 24/7. spray down the condesor in the front of your car with a hose and then it might cycle. your kilma is working fine... fill the system up with a little more freon you cant tell by pressures on the low side anyways. Check your sight glass on your reciver drier if you see bubbles in the eye glass when at idle on the air on high, with the outside vent on then you need more freon.

I dont care what anybody says about how thats not the correct way to do it. It gets the job done.