New to the site here so be patient with me.  I have been wanting to join this site for awhile so this is as good an excuse as any.

The last two mornings I have seen what looks like vapor/smoke coming through my A/C or Heater vent.  It is very light and almost unnoticeable but it drives me nuts.  It only lasts about 15 seconds or so and is very light.  It does not have a smoky smell it is more of a light musty smell but it is very faint you have to get your nose directly in it.  Comes on when the truck is fully warmed up at 190 degrees.  My blower motor is not on at all the heat dial is set to heat.  When I drive throughout the day the problem never happens again.  I think it is a small leak in my heater core that when my truck gets up to temp it vaporizes through the vent.  I do not have a noticeable leak in the heater core (aka no antifreeze on the passenger floor) and my coolant level has not dropped noticeably.  No overheating issues.

A little background...about a month ago I drained and flushed my Cooling system per Mikes directions on this site.  Prior to the flush I was not getting my temp over 160 degrees which turned out to be a bad Thermostat.  Now I am getting around 190 degrees constantly it has been nice to have real heat.  My thoughts are my Heater Core may have been doing this for awhile which I never noticed or never vaporized due to not reaching temperature, or the flush jarred something loose (hadn't changed my fluid in 100k miles don't throw stones).  Just wondering what you all think, I feel I am pointing in the right direction. 

 

Don't know how to add my Vehicle info on here yet so here is a quick rundown of what I think is important:

1999 Ext Cab, 5 -Speed, 250 K Miles

 

Does the vapor smell sweet?

There is not much smell to it like I said it is not very much vapor at all...smells a little musty most definitely not smoky that is for sure.  Cab does not have the strong sweet odor a larger antifreeze leak would give off, I know what you are asking. 

Humm,

 

I have had this happen before in some of the older BMW's that I had , but that was typical of them.  

 

Has it been humid in your area as of late?  

 

 

Even a drip leak in the core should make the cab smell sweet so I am not thinking you have a core leak.  Rather I think you may be having a build up of moisture due to humid days and cold nights.  But I am taking a shot in the dark and just guessing.  

I live in Utah not really humid here at all, days lately have been in the mid 70's with lows in the 50's.  It is really odd I know.  I need to replace my Dash in the near future it is in shambles I have been putting it off so I am thinking of doing the Heater Core, Evap, Blower Motor and Resistor while I have access in there.  I know these items cost but when in Rome...... 

Yea if you are going to pull off the dash you might as well.  

 

very strange.

 

really until you can take a peak at the core I would ignore it.  

Have you tried to put your temp control to cold to see if you still get the vapor?

Yeah I played with the cold setting a little bit and it ran fine.  I will set it to cold first thing in the morning to see how it reacts.  Thanks for the responses so far.

Drain for the HVAC plugged up and holding water in the bottom?

 

Like @Me78569 said heater core should give off a sweet smell as the vapor blows off. About 90% of the time those kind of issues end up being the heater core. The only other moisture would be the A/C side and it holding moisture in the drain area because of blocked drain. Other than that there is no other moisture or water source in the HVAC system.

I am convinced it is the heater core at this point.  Had the temp setting on cool for about 10 min or so (at full temp, no blower on) as soon as I moved the tem setting to hot instant vapor for about 10 or so seconds with the sweet scent of coolant in the air haha.  It is not a big leak so I am going to do some research and then order a bunch of parts before tackling.  Mike I have seen your instructions as to how the dash is moved out of the way and I fully agree with the advice of pulling the entire system to clean it out rather than hacking in just a new heater core.  I have a couple of questions you all may be able to help with before I dive in, as the engineer in me will not tackle things until I know fully that I have all knowledge/tools available to me.

 

1.  New Dash:  I have done some research, it looks as though the LMC Dash is the best value for the product.  Does anyone have a different/similar opinion they would care to share?

2.  AC Evap:  Two things here how tough are the AC lines to the Evap to get off?  Special tool needed at all?

3.  AC Decharge and Recharge:  How much does this cost to do have a professional evac the system and later recgarge?  This is something I have never messed with.  To be honest it makes me nervous to even touch my A/C system it has ran like a champ for over 14 years.  Any advice in this arena would be helpful.

 

 

1. I've never had to do a dash yet for either my 96 or my 02 yet... So I can't answer that.

2. Yes there is a special tool it about $8 fro Napa and its just a plastic collar you push into the spring lock and pull the tube off.

3. I typically charge $40 labor and what every the price of freon is for about 2.5 can (12 oz). As for recharging you need to be able to pull a vacuum on the system to remove moisture.

 

I've rebuilt several Dodge Ram A/C systems not hard just time consuming.

I put the LMC dash in mine about 3 years ago. It fit well and looks just fine. I am very happy with it. Some of the screws you have to install on the driver side are PITA to get to since you hinge the dash on that side. Put the new dash on before reinstalling the HVAC box. An extra pair of hands for those screws is very helpful. The skinnier the better.  

When I did the heater core on my 96 I didn't evacuate the AC. System.  If you remove the brackets that hold the lines against the fender well and the back of the engine bay you can get the new heater core in.  

 

I only had had a sweet antifreeze spell in mine occasionally over a period of a couple of years. The radiator was never low on coolant.  After looking for the antifreeze smell for a year I decided to replace the core. Didn't want it to start leaking a lot if I was on the road. 

 

I used a NAPA core for mine.

 

Bob

 

1. LMC Dash, bezel and front grille. Fit and quality are great. There is a slight color difference but still looks great!

Special thanks to TBO for installing it for me!

 

 

@ unioncreek I appreciate the advice however I am going to evacuate the system and replace the Evap while I am doing the job.  This allows me to pull the entire HVAC box as well to clean, lubricate and inspect.