Warm AC when still, cold AC when moving. What gives? - Page 2 - PeachParts Mercedes-Benz Forum

leathermang · #16 07-12-2011, 10:00 AM

I beg to differ... since THE bottle neck on all AC systems is Air Flow Across the Condensor....
If he had one of those Northern Tool Blowers sitting at his front bumper.. he could get cold air at an idle.
Sufficient air across the condensor ( meaning excess sometimes ) can make up for a lot of deficiencies in the rest of the system....

marco5 · #17 07-12-2011, 11:12 AM

I'm having this exact same problem, can someone help out? I wont ignore the post lol.

I filled the system without having is vacuumed first, installed a new AC dryer... I won't make that mistake again.

While Driving I have colder air then up north, but at stop its warm as the air outside. Can anyone give advice or tips on what I/WE should do?

BTW: Compressor stays engaged at idle and I'm using R134A.
1986 Mercedes 300D.

I guess I can try cleaning my consensor next.. before having the system vacummed.

leathermang · #18 07-12-2011, 11:42 AM

Ok... just to make sure we understand each other.. when you say you did not vacuum it first... you are not referring to Flushing it... but are saying you installed the refrigerant without pulling a vacuum AT ALL ?
Cleaning the condensor and the radiator and making sure their fins are straight is needed no matter what .. even on a good working system it make the compressor work less often.. just good house keeping..
Basically you need to take out what you have... vacuum it so you have no moisture in the system ( for several reasons ) , install new rec-drier , but I also highly recommend that you pressure test before vacuum so that you do not lose your refrigerant or have to pay to have it recovered and have to buy a new rec-drier AGAIN...

marco5 · #19 07-12-2011, 12:25 PM

Can I have it vaccuumed with using the brand new dryer I just got? Its still working pretty good, I dont really want to spend on a new dryer.

Would completely flushing the system (aka vacuuming it), having a shop refill it work without replacing the AC dryer?

leathermang · #20 07-12-2011, 01:17 PM

You are welcome to shoot yourself in the foot by not paying what ? $30-40 dollars for a new rec-drier....

It is your money and you are the one that is hot.... If you are wanting to have it potentially last a long time..... you need to put in the new Rec/drier....this is SOP anytime a system is opened up or is known to have been compromised by a leak...

Flushing the system is Totally different from vacuuming it...

First you need to go to the sticky at the top of the page and study the whole thing.. you will get a much better picture of the overall situation and be able to ask questions...

Diesel Dawg! · #21 07-12-2011, 04:40 PM

Multiquote isnt working for me so I'm doing it manually:

Quote:

R134A or R12?

Have you put gauges on the system?

R134, no I haven't put gauges on it.

[QUOTE] How long has the situation been going on ?
Was this sudden or slow to develop ?[QUOTE]

It has been like this since I got the car ~1year

[QUOTE]Your car is 28 years old. Have you ever cleaned the radiator and evaporator fins?[QUOTE]

Yes I have and they look clean

[QUOTE]
There have been a few other threads with SD's saying the compressor is cutting out. Maybe not an airflow problem, but a compressor relay-engine RPM problem?

Does the compressor stay engaged at idle?[QUOTE]

Yes it stays engaged

[QUOTE] This is the second OP in the last week that posts a question... stays on the site long enough for several people to ask legit questions trying to help..
Then goes offline without answering the questions...
At the time I posted he was still online...
I even PM'd him when I saw that he was online and had not answered 79Mercy's question yet...[Quote]

Calm down man. Not everyone can sit here and hit the refresh button for hours on end. I've got a hectic schedule and am lucky if I get the time to post a question or a response to help someone else out.

[QUOTE] How's your fan clutch?[QUOTE]

Good question....seems to be fine...resistance when spun manually, blows a bunch of air with the engine on....not sure how else to check it...

[QUOTE]improving condenser airflow can make some difference at idle, but NOTHING beats RPM for improved cooling from the system.[QUOTE]

I raised the rpms at a stop to 2500 or so just for the fun of it....it didnt seem to blow colder like it does while the car is moving

[QUOTE] If he had one of those Northern Tool Blowers sitting at his front bumper.. he could get cold air at an idle. [QUOTE]

I think so too!

79Mercy · #22 07-12-2011, 04:48 PM

You need to get gauges on the system, without knowing the pressures there isnt much to do yet. Harbor freight sells a inexpensive set of gauges, not the best but they should work for the little bit you'll need them.

1980sd · #23 07-12-2011, 07:09 PM

On my car (1980 300SD with ACCII) there are only 2 things that can cycle the compressor while the system is running. The Low-pressure cut-off switch (On the high pressure line at the drier.) and the evaporator temperature regulator (On the evaporator).

The low pressure switch disengages the clutch when the hi-side pressure is too low. The ETR disengages the clutch if the evaporator begins to freeze up.

Neither should cycle during normal operation if everything is A-OK.

Your car may have other things but I'm sure it has an ETR.

Mine cooled LIKE A BOSS going down the road before my compressor crapped out but fell on it's face at idle.

Yak · #24 07-12-2011, 08:30 PM

[QUOTE=Diesel Dawg!;2750579]Multiquote isnt working for me so I'm doing it manually:

[QUOTE] If he had one of those Northern Tool Blowers sitting at his front bumper.. he could get cold air at an idle.

Quote:

I think so too!

Having ruled out most other obvious ideas, sounds like airflow. A good shop should use the big blower in the bay to simulate on-the-road conditions. I thought I read on the forum here about someone using a fan/mister combination to simulate more airflow in the garage.

You could make sure the gap between the condensor and radiator is clear of bugs/debris, maybe swap to a different electric fan from a JY.

Does the temp gauge correspondingly climb at idle/low speed to indicate less flow across the radiator while trying to dissipate condensor heat? If so, then I'd definitely say it's a fan problem.

1980sd · #25 07-12-2011, 08:45 PM

[QUOTE=Yak;2750681][QUOTE=Diesel Dawg!;2750579]Multiquote isnt working for me so I'm doing it manually:

Quote:

If he had one of those Northern Tool Blowers sitting at his front bumper.. he could get cold air at an idle.

Having ruled out most other obvious ideas, sounds like airflow. A good shop should use the big blower in the bay to simulate on-the-road conditions. I thought I read on the forum here about someone using a fan/mister combination to simulate more airflow in the garage.

You could make sure the gap between the condensor and radiator is clear of bugs/debris, maybe swap to a different electric fan from a JY.

Does the temp gauge correspondingly climb at idle/low speed to indicate less flow across the radiator while trying to dissipate condensor heat? If so, then I'd definitely say it's a fan problem.

So is that how you do it? Check the pressures at idle and then with the fan to simulate rockin' down the highway and compare them? Adjust the charge?

I don't have a vacuum pump or gauges but I have a big powerful squirrel cage blower. It's powerful enough to blow a little guy like Greg over but it won't quite blow a grown man down. Still pretty powerful...

Yak · #26 07-12-2011, 09:50 PM

Should you NEED to use a large fan to work on A/C? Probably not. But if you're troubleshooting warm vent temps on a R-12-to-134a converted system and you're trying to get the proper charge into the system, and it's Texas hot in the summer and your car is sitting in place and they're revving the engine to about 1500-2000, it may help the process - and keep the tech cooler.

Pressures are usually checked a bit above idle. I recommend reading here (quick and easy) for gauge use: http://www.aircondition.com/tech/questions/82/

Here is also pretty good: http://www.denlorstools.com/autoblog/2009/04/adding-freon-to-car-ac-gauge-readings-explained/

The second link includes other possible explanations for not-quite-heart of the envelope gauge readings. For example high pressures might be an overcharge or "also can indicate that the condenser fan is not working, is too slow or the car is overheating and heat is transferring from the radiator to the condenser."

leathermang · #27 07-12-2011, 09:56 PM

What Yak said X2.