AC blows warm under acceleration

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DoubleJ

Member
57
29
18
According to the internet, if your AC blows warm when you accelerate, it's most likely a low charge. I'm showing 37/245 PSI on a 90 degree day. The only source I could find said 35/225 max, so I'm not undercharged.

What else could it be, some orifice?
 
I had the same problem on my 88TC. Looks like yours is a 2011? Turned out to be two things: stuck vacuum check valve and broken vacuum line. On my car, the vacuum to control the HVAC is pulled through a vacuum check valve behind the intake. (Picture 2 and 3). Notice the bug just chilling on my check valve, the black and white thing. The check valve hooks to a little plastic manifold that connects to a vacuum canister (The soup can thing in picture 1) that stores vacuum for the HVAC during acceleration. Maybe along with AC turning warm under acceleration you HEAR a blend door actuating? Maybe not, but I did. When I was working on this issue I located the check valve and found it was stuck. Could suck through it both ways, even after shooting solvent through it. I replaced that and the issue got better, but not all the way. I started tracing my vacuum lines and found the one going to the canister was broken clean in half. Stuck a new one on and the AC blows cold all the time. Problem solved. Let me know if this helps.

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DoubleJ

Member
57
29
18
That soup can brings back some memories, all of my 70s Marks had the same thing. I'll give a listen for a blend door moving, maybe have kid climb under the dash and use her good ears. I know those older Lincolns were vacuum everything, even the headlight covers on my Mark IV and Vs were vacuum actuated. Not sure about these newer cars, they're not quite as fancy as the older ones. I don't even have a thermometer in my mirror.
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I only mention the blend door because one of mine makes a little creak when it closes. I kept hearing it during acceleration and put two and two together: total loss of vacuum in the HVAC. I had my AC charged and checked out before this problem happened to me. While cruising the AC would blow like ice, put my foot into it and it would turn warm.
 

Hound Dog

Member
90
47
18
Do these cars shut off the compressor under hard acceleration? I have not noticed. I know my 80's mustang that was carburated had a switch that would get hit at WOT to shut off the AC compressor.
 

DoubleJ

Member
57
29
18
My 97 Mark VIII did, but only at WFO. This town car is blowing warm under mild acceleration. Basically anything in the neighborhood of generating a down shift.
 
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