was that supposed to happen?

(2001 Dakota, 4.7l v8 engine. I've mentioned the AC before.)
Ok, so it's already known there's a leak somewheres in my AC system. Mechanic recommended waiting until spring to fix it. I attempted to
fill it in the fall, went through a can and a half of refrigerant before I gave it up as a bad job (gauge never read sufficient pressure).
Was able to use my defroster the entire winter with no probs until Friday, when the motor started making noises again.
So, on this beautiful Sunday afternoon, I went back out with my can and gauge, popped that lead off the cannister and shorted it, fired up the truck and loaded more refrigerant. All was going as expected - the gauge indicated slight increase in pressure but still not enuf - when suddenly the truck made a noise like the AC came on - or off, or something - and the pressure gauge shot up to full.
Was that supposed to happen? I immediately stopped, turned the truck off, set all to rights - and heard an extended hissing like air escaping in the engine - sounded like it was below where the low pressure valve is, but closer to the engine block. Eventually it faded. When I fired her back up, the AC - for now - is working properly. But why did it suddenly... I'm not a mechanic you understand, so I'm not quite sure *what* it suddenly did.
Last time I spent a lot more time trying to load r134a in, and the engine/AC sound never changed the whole time. I've no idea if the fact that it did this time is a good thing, or a bad thing!
Oh, and does $1500 to fix the leak, which I'm told is in something behind the firewall(since I can't find dye around the engine block) a fair price? Seems high to me.
Any advice appreciated!
Jodi
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I don't really know but am guessing that there is a low pressure switch in the system. By adding refigerant you closed the switch and the compressor came on..
beekeep     
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Well, she shorted out the low pressure switch at first (that's the connector she took off the accumulator).
Jodi, did the AC compressor kick on when you first shorted out the low-pressure switch?
And the $1,500 charge is to remove the dash, and change out the A/C evaporator - which are known to go bad and leak. $1,500's a little high for that, though - usually it's about $1,000 or so. It is a lot of work removing the dash - by the time they get it out, drain the coolant, recover the A/C, get the heater box out and apart, swap the evaporator, put it all back together, and re-fill coolant and A/C, it's probably taken them the better part of the day.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Suddenly, without warning, Tom Lawrence exclaimed (4/6/2009 7:33 AM):

Tom, thanks. When I did this in the fall, I knew the names of all the parts I was working on, and why. Memory's horrid though but yes, I shorted the low pressure switch to keep the AC from cycling on (or is it off)? That's why I was so surprised when it did it anyway.
That's what I though - around $1,000. This is DC though, where Things Are Very Expensive (just ask my cat, I've put $900 into her medical bills this month, with another $700-900 to go). Or don't ask her - she'll just tell you I haven't fed her yet (even if I have).
Who needs a mortgage? Medical bills for me, my cat, and my truck are what's chewing into my nest egg. ::sigh::
jmc
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
The noise was the high pressure relief valve opening (usually is located on or near thr compressor. Your orifice is problably partly clogged and your suction pressure will be low. You added refrigerant to bring the suction pressure up........it couldn't get to normal, so you overfilled it and the relief valve blew. After the pressure is reduced the valve seals itself off and lucky for you it sounds like the charge is about right or it would not be cooling. FWIW I spent two weekends on my wife's cavalier installing a new evaporator. I would be hard pressed to take on another one for $1500. I don't know how a dakota would compare. I think it would be easier due to more room. I am not a mechanic just a do it yourselfer (commercial refrigeration servicman by trade). :-) If you decide to tackle the evaporator you will have to obtain a manual (hardcopy or online) and find the procedure for disabling the airbag system. If you get prying around under the dash you may deploy the airbags. At that point you will care little about the A/C. You will be paying a proffessional to repack the airbags. Repair manuals don't cover this...........they all say: Seek professional help in this matter. :-) Good Luck Lyndell

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Suddenly, without warning, Lyndell Thompson exclaimed (4/6/2009 9:37 PM):

> The noise was the high pressure relief valve opening (usually is located on > or near thr compressor. Your orifice is problably partly clogged and your > suction pressure will be low. You added refrigerant to bring the suction > pressure up........it couldn't get to normal, so you overfilled it and the > relief valve blew. After the pressure is reduced the valve seals itself off > and lucky for you it sounds like the charge is about right or it would not > be cooling. FWIW I spent two weekends on my wife's cavalier installing a new > evaporator. I would be hard pressed to take on another one for $1500. I > don't know how a dakota would compare. I think it would be easier due to > more room. I am not a mechanic just a do it yourselfer (commercial > refrigeration servicman by trade). :-) If you decide to tackle the > evaporator you will have to obtain a manual (hardcopy or online) and find > the procedure for disabling the airbag system. If you get prying around > under the dash you may deploy the airbags. At that point you will care > little about the A/C. You will be paying a proffessional to repack the > airbags. Repair manuals don't cover this...........they all say: Seek > professional help in this matter. :-) > Good Luck Lyndell >
Cool, thank you for the explanation. I always like to know the "why" of things. I have no intention of handling this myself, I can fix small stuff but this is definitely outside my experience or comfort level!
I know my passenger side airbag has a way of disabling it using the key (no babies so I've never tried it), but no idea if this is sufficient for ripping the dash apart. I'll let my trusted mechanic worry about that, it's apparent they've worked on Daks before and have also told me this is a common enough problem with this truck.
Goes in Monday after next to get this fixed. I've lived hereabouts summertime with a vehicle or two with no AC, but I'm not interested in doing that any more :)
jmc
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.