Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

LinkBack Thread Tools Display Modes
Old 11-03-2008, 02:41 PM
C280 Sport's Avatar
Registered User
Join Date: Sep 2008
Location: Saratoga Springs, NY and Sarasota FL
Posts: 152
Hissing sound comming from the A/C

2002 E320. The AC makes a hissing sound once in a while. I took it into the shop and they said it blows cold and everything is fine. I told them it might me freeon. They said there is nothing wrong and it blows cold. I think I might have a leak? Or could it really need freeon?
Reply With Quote
Old 11-03-2008, 02:57 PM
Registered User
Join Date: Oct 2005
Posts: 4,263
There is only one way to know for sure if you are low on refrigerant (but technically, what you use is called Suva rather than Freon), and that is to reclaim and weigh what is in there now.

Has the system been serviced in the past? It will naturally leak a bit, so if it is the original charge it is likely to be low. Low refrigerant level causes insufficient oil return to the compressor before it causes the system to start to blow warm. Insufficient oil return causes compressor damage.
Reply With Quote
Old 11-03-2008, 05:31 PM
Registered User
Join Date: Jan 2003
Location: Dallas
Posts: 777
I've seen a lot of AC units hiss from time to time; usually when you kill the engine, but many times when the compressor cycled on/off while modulating the temp in the car. I always assumed it was normal noise from the expansion valve; but come to think of it, I don't think my MB has ever hissed. But, if the shop checked the pressures and they were proper, and it cools well, I guess we could assume the freon is sufficient. Since the acumulator holds the excess freon, and is on the high side, and the compressor gets it's freon/oil supply from the low side, I would again assume that the expansion valve is flowing all the freon/oil the system is requesting, and all should be fine.
Doing a lot of logical "assuming" though, I'm certainly not an AC guru.

Reply With Quote
Old 11-03-2008, 07:13 PM
Registered User
Join Date: Oct 2005
Posts: 4,263
The problem is that while the refrigerant does return, the oil doesn't do so well in an undercharged system.
At the top of the list: A “just-low”
refrigerant charge (typically a 10% to
20% undercharge) significantly reduces
oil flow, according to Four Seasons’
Jim Johnson. He gave this example
for 88F ambient: The a/c duct
temperature rose just 3 (from 46 to
49F), hardly enough for a customer
complaint. Yet so much oil was
trapped in the evaporator under lowrefrigerant
conditions that oil circulation
dropped from about 10% to 25%
by weight to just 2% to 4%. That’s a
prescription for increased compressor
wear and therefore short compressor
life. Other causes of similarly low oil
flow, he said, are internal restrictions
(typically from contamination, which
increases rapidly with low refrigerant),
poor airflow through the condenser
and high coolant temperatures.
They're writing about a level of refrigerant loss that will NOT result in customer complaints, until the compressor eventually fails.
Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 04:25 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page