withbag

Hi,

I have 2006 E350 Base and I hear a hissing sound on and off continuously when heating is on. If off, no sound at all.

Something no hissing at all for whole driving time with heating is on. Sometimes hissing sound starts about minutes after heating is on.
Sometimes hissing starts right after heating is on.

What would cause the sound?

Thanks,

Eric

Plutoe

Wow hissing sounds are very popular this week,in any event run the car around with the heat and blower on high, then lift the lid and in the left rear corner is the duo valve-------is the hissing coming from the valve????

If so replace the valve or find the little sausage maker over at kiddy benz who claims he spends hours to clean the valve then forgets how to put the valve back, but claims it's a simple DIY!!

RCPDesigns

Maybe there is a snake in there and it gets mad when you turn the heat on...

withbag

I don't hear hissing sound from there..another guess?

Plutoe

Once again I am confused---so before lifting the lid it hissed and then when you opened the lid there was no hissing or it did hiss but you failed to tell us where the hissing was comming from----am I correct---if so it only hisses when you are driving

withbag

I hear hissing from the far-right vent and I try to hear hissing from where duo valve is but I did not hear from there. I came back inside and hissing is still there. Do you have another idea? Thanks in advance.

withbag

Plutoe,

I did it again and I now hear hissing sound around where duo valve is. Pluteo, why do you think the sound comes out on and off? do I have to replace it? Is it DIY-able if I am able to do oil change? Thanks in advance.

Plutoe

The duo valve is like your toilet bowel water inlet on off valve---To experience the hissing. Have your butler turn off the water on a toilet, then if his job description allows, have him flush the toilet---now to refill the bowel have him slowly open the water inlet valve---as the bowel fills you should hear a shrill of a sound until the valve is opened to the point where the volume of water stabilizes and the shrill goes away.

Your issue is that the duo valve is on the outlet side of the closed hot water heating circuit. In the heating mode the duo valve opens slowly in response to the cabin temps you select---the hotter or colder the driver/passenger requirements are the valves open and close to meet the heating requirements and it sounds like one of the valves is vibrating producing the hissing noise.

Remember I am 1300 miles away from the car and that is where I would start-----turn the AC on do you still have hissing, if you do it ain't the duo valve, if you don't then I would suspect the duo valve.

The valve body of duo valve can be removed and cleaned----but be careful of the source there are loads of DIY info on the subject, but I have found most to be erroneous, especially the one written up by the sausage maker at brand x

withbag

With AC on, there is no sound at all so your guess could be right 100%. Do you think it would be possible to bring to a Pepboys or Sears and pinpoint 'replacement of duo valve'? Thanks in advance.

Plutoe

I go to PepBoys for tires and to Sears for washing machine parts----never thought of taking my smoker to either one of those places except to put the tires and washing machine parts in the trunk---never knew they repaired cars!!

However I will suggest both to my ex wife!!