Replacing HVAC unit? Install help, please!

MMM2003

MMM2003

Contributing Member
Hey:

It looks like I need to replace my HVAC (Heating/Venting/Air Conditioning) unit on my MM. I'm only getting cold air on the Defrost and Floor setting. The air flow never changes to the VENTS.

I got a price from Ray and was wondering if this is a DIY project? Has anyone done this? How tricky is it to get the unit out and what are the connections like (Plug and Play)?

Any help, pictures, advise, or simple instructions would be greatly appreciated.

Thanks in advnance!

Peter aka MMM2003

P.S.: I checked and this is not covered under my extended (basic) warranty.
 
Hold on just a sec...
Just got ahold of a parted out car, all that stuff is in my garage.
PM on the way.
 
Just had to change mine out a couple of weeks ago. Relatively straight forward change out.
First take off the trim strip (dot matrix pattern stuff) by hooking your fingernails under one end and pulling the trim off gently. If you have a separate clock, it will have to be unplugged after removing the trim. Mine had sufficient wire, so it wasn't a problem. The unit then has 4 7 or 8 mm nuts that hold it in (don't remember which) and the unit will slide forward.

The back has 2 electrical snap in plugs, and one for the vacumn lines. (The vacumn lines are held in place by 2 screws, not snapped in.) Swap out units, checking to make sure vacumn lines are not crimped, reverse process, and you back in business. About 10 minutes total.
 
Second Wind said:
Just had to change mine out a couple of weeks ago. Relatively straight forward change out.
First take off the trim strip (dot matrix pattern stuff) by hooking your fingernails under one end and pulling the trim off gently. If you have a separate clock, it will have to be unplugged after removing the trim. Mine had sufficient wire, so it wasn't a problem. The unit then has 4 7 or 8 mm nuts that hold it in (don't remember which) and the unit will slide forward.

The back has 2 electrical snap in plugs, and one for the vacumn lines. (The vacumn lines are held in place by 2 screws, not snapped in.) Swap out units, checking to make sure vacumn lines are not crimped, reverse process, and you back in business. About 10 minutes total.
Click to expand...

Cool. Thanks! Sounds like something I should be able to do.

Peter
 
I have the same problem, and was told it was a vacuum leak, which I have been unable to find. How do you differentiate between needing a new unit and a vac leak?

My problem is all over the board. It only blows out of the def only, then only out of the floor, then if I hit a certain speed and mess with the manual fan spoeed dial, it comes out of the vents. its really driving me crazy, but don't want to throw a bunch of money away on troubleshooting time.

anyone have a recommendation as to where to start looking for a vac leak?
or is this a unit problem?
 
I was going to post that if the vacuum reservior was not holding vacuum or not receiving vacuum, it would also resort to a failsafe condition, and changing the ETAC module would not cure that, and then we get word that it did fix it on one car! Well, I would check the vacuum res. under the hood first. Pop off the hose and see if vacuum exists in the line. At the same time, you could also run the engine, shut it off, then pull that hose to see if any vacuum was stored, indicated by a rush of air being inhaled into the res. It is on the left side underhood, a squarish box that stands atop the wheel area, around 6 or 7 inches square. Good luck.
 
Have you moved or rerouted anything under the dash or hood that could have crimped or pulled a vacumn line? Our cars are not quite old enough, although it is possible, for the lines to dry rot yet.
The HVAC unit for our vehicles, on the other hand, are notorious for going bad. I tested mine by running a vacumn line from the engine to the differnent vacumn ports that plug into the back of the HVAC unit. Once I was satisfied that all the doors opened and closed by manually rerouting vacumn in this manner, I was pretty sure it was the unit and not a vacumn leak somewhere
By the way, a regular (non automatic) heater/AC controller from a Crown Vic, GM , etc. will slide right in and work just fine. You will lose the automatic function, however.
 
Second Wind said:
Have you moved or rerouted anything under the dash or hood that could have crimped or pulled a vacumn line?
Click to expand...

Nope, haven't done anything under the dash or hood for quite a while, but I will double check. Only place I worked on was under the steering column.

Second Wind said:
The HVAC unit for our vehicles, on the other hand, are notorious for going bad. I tested mine by running a vacumn line from the engine to the differnent vacumn ports that plug into the back of the HVAC unit. Once I was satisfied that all the doors opened and closed by manually rerouting vacumn in this manner, I was pretty sure it was the unit and not a vacumn leak somewhere
By the way, a regular (non automatic) heater/AC controller from a Crown Vic, GM , etc. will slide right in and work just fine. You will lose the automatic function, however.
Click to expand...


Hmh. Interesting. I have some vacuum hose around somewhere and have to try that before replacing the control unit.

Thanks for the info.

Peter
 
Last edited:
mtnh said:
I was going to post that if the vacuum reservior was not holding vacuum or not receiving vacuum, it would also resort to a failsafe condition, and changing the ETAC module would not cure that, and then we get word that it did fix it on one car! Well, I would check the vacuum res. under the hood first. Pop off the hose and see if vacuum exists in the line. At the same time, you could also run the engine, shut it off, then pull that hose to see if any vacuum was stored, indicated by a rush of air being inhaled into the res. It is on the left side underhood, a squarish box that stands atop the wheel area, around 6 or 7 inches square. Good luck.
Click to expand...

Thanks for the info. I'll check on that as well.

Peter
 
While it seems you're on the right track with a vacuum leak chase down, it may be the HVAC control head as it's been talked about here. This explains a transient break down, sometimes it works right, sometimes not.

However, if your A/C never, ever comes on right and it's stuck either in the defrost mode, or, strictly the vent mode even when you want it in defrost mode, or, go for heat rather than A/C, it's a "blend door motor", and the worst possible repair of the HVAC system. The "blend door" is actually powered by an electric servo motor that's vacuum actuated. You could have all the correct vacuum leading to the switch, but the motor is burned up, and stuck in the last position it was in prior to break-down.

The benefit to owning 3 Marauders over time, has been the "delight" to trace and repair the HVAC from many angles. The blend door is the worst of them, the dash has to come out. Hopefully one of our resident repair techs will join in with some advice?

Maybe you can do this repair yourself, but it's not pretty, I suggest you start with a bit of research into a "big red book" somewhere. Try to rule this out before you get too deep into alternative repairs suggested here?

Just my .02c, carry on gents...
 
I had the no A/C from the dash vent problem. Dealer tried to tell me the 3rd party audio install pinched a hose. 90,000 miles ago! Left the car overnight and they decided the module was bad. Good thing I have a 100k warranty. Retail for the part is $480!
 
Well:

I started to check into my HVAC problem. It is truely very easy to get to the unit and replace it if necessary. I'll have to do it again, since I a) didn't bring a vacuum hose home to test the individual doors and b) didn't have my camera to take pictures of the repair.

I did notice that none of the doors open individually, no matter which setting I use. It's always blowing out of the Defrost and Floor. THis makes me think that the HVAC control unit is bad.

I was able to manually push the "vacuum solenoids*" (for lack of a better term) and switch between FLOOR and DEFROST only. The other ones are not accessible without removing the dash.

*= Round silver valves with two ports, connecting to the HVAC unit and a manual override bar, located behind the HVAC unit under the dash.

I'll post more later.

Thanks for the help so far.

Peter aka MMM2003
 
I tested my control unit today with the vacuum line from the engine compartment, and confirmed that it is the unit. The vent doors open fine when I manually apply the vacuum line to the appropriate hose. I'll post some reference pictures with a "How to" later.

Thanks for all the advice. All I need now is a new HVAC control unit.

Thanks,

Peter aka MMM2003

Second Wind said:
Have you moved or rerouted anything under the dash or hood that could have crimped or pulled a vacumn line? Our cars are not quite old enough, although it is possible, for the lines to dry rot yet.
The HVAC unit for our vehicles, on the other hand, are notorious for going bad. I tested mine by running a vacumn line from the engine to the differnent vacumn ports that plug into the back of the HVAC unit. Once I was satisfied that all the doors opened and closed by manually rerouting vacumn in this manner, I was pretty sure it was the unit and not a vacumn leak somewhere
By the way, a regular (non automatic) heater/AC controller from a Crown Vic, GM , etc. will slide right in and work just fine. You will lose the automatic function, however.
Click to expand...
 
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