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2003 Grand Marquis AC blows warm hwy speeds


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johnnydollar79
Novice

Jun 12, 2022, 12:25 AM

Post #1 of 18 (424 views)
  post locked   post icon 2003 Grand Marquis AC blows warm hwy speeds  

2003 Mercury Grand Marquis 4.6

I’ve been fighting this problem for 6 months. It started when I replaced a noisy AC compressor in my car. I also replaced the condenser and the orifice tube. I put a vacuum on it for over an hour and then recharged by weight. Since then I get fairly decent cooling below 45mph but when I go above that, it starts blowing warm. I did drive it on the freeway with the gauges visible and this is what’s happening, as far as I can tell…The high pressure side is rising sharply until the high pressure cut-off switch kicks the compressor off at 400psi. When the needle is making its climb to 400, the low side is going too low (about 38 psi on a 105 degree day). It keeps repeating this cycle which means the compressor is only running for seconds at a time. I’ve taken the system apart three other times looking for the cause, and each time I put a vacuum on it and recharge by weight.

I really hope someone can help me. Thanks in advance!


Hammer Time
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Jun 12, 2022, 3:45 AM

Post #2 of 18 (401 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

How much refrigerant are you putting into it?



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johnnydollar79
Novice

Jun 12, 2022, 6:18 AM

Post #3 of 18 (395 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  


In Reply To
How much refrigerant are you putting into it?



38oz per the label in the engine compartment.


Hammer Time
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Jun 12, 2022, 6:25 AM

Post #4 of 18 (388 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

Everything you are describing is pointing to an overcharged system. It's always possible some of the parts you replaced have reduced capacity causing this.
You didn't post what your pressures are at idle but I suspect they are both higher than they should be.

I would try bleeding off some of the refrigerant a little bit at a time and see what it does for your pressures. It doesn't take much overcharge to cause pressures like that.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



johnnydollar79
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Jun 12, 2022, 6:36 AM

Post #5 of 18 (384 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  


In Reply To
Everything you are describing is pointing to an overcharged system. It's always possible some of the parts you replaced have reduced capacity causing this.
You didn't post what your pressures are at idle but I suspect they are both higher than they should be.

I would try bleeding off some of the refrigerant a little bit at a time and see what it does for your pressures. It doesn't take much overcharge to cause pressures like that.


Sorry. According to the R-134A chart, the pressures are actually a hair low but steady at idle. 48 & 315 at 105 degrees ambient.

So some aftermarket parts have smaller capacity?


Hammer Time
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Jun 12, 2022, 6:43 AM

Post #6 of 18 (378 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

I don't know what chart you are looking at but throw it away.

First, there are numerous variables such as the ambient temp you refer to but also blower speed, condenser condition and condenser fan speed.

I am a tech in South Florida that has specialized in AC repair for the past 30 years. I have done literally hundreds of these systems and I'm telling you your pressures are WAY too high.

I would expect to see pressures closer to 200-225 over 35-40 at idle. It's no wonder you are hitting the high pressure cutoff.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



johnnydollar79
Novice

Jun 12, 2022, 7:03 AM

Post #7 of 18 (364 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  


In Reply To
I don't know what chart you are looking at but throw it away.

First, there are numerous variables such as the ambient temp you refer to but also blower speed, condenser condition and condenser fan speed.

I am a tech in South Florida that has specialized in AC repair for the past 30 years. I have done literally hundreds of these systems and I'm telling you your pressures are WAY too high.

I would expect to see pressures closer to 200-225 over 35-40 at idle. It's no wonder you are hitting the high pressure cutoff.



This is a link to the chart but hundreds of other websites have it too. I live in Phoenix so ambient is crazy.

https://www.acprocold.com/faq/r-134a-system-pressure-chart/
My dad is actually an automotive instructor and was a mechanic for 25 years before. He has been stumped by this which is why I’m reaching out for assistance.


Hammer Time
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Jun 12, 2022, 7:07 AM

Post #8 of 18 (354 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

I'm telling you what your problem is but you're not listening.

There is no scenario where 300PSI is OK at idle. The compressor was not made to push that much pressure consistently and will fail faster than you can order a new one.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jun 12, 2022, 7:11 AM)


johnnydollar79
Novice

Jun 12, 2022, 7:12 AM

Post #9 of 18 (348 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

I will definitely try to let off a little bit of the refrigerant and see what it does. I truly appreciate your help. I was only trying to let you know the background and information I was going off of. Again, I thank you for the suggestion.


Hammer Time
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Jun 12, 2022, 7:28 AM

Post #10 of 18 (331 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

When you bring it up to 2000RPM, the pressure should not exceed 300 PSI. Even that is a little on the high side. Most I see will stay under 275 when doing that.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Jun 12, 2022, 8:59 AM

Post #11 of 18 (295 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

Said by Hammer it's WAY overcharged. Rules change when that hot IMO in New England hits that just not for long ground is too cool to stay there.
New parts can and will reduce system capacities should say so when purchased by how much but don't. This car could be done by touch and feel or with a trusted infrared thermo.
High should be about 2.5X the temp actually coming into the grille as measured in front of it also at a raised idle - say 1,500. Have a remote in center vent you can see performance is what we are after without blowing system up.
Refrigerants are pretty exact pressure to temperature such that if you know one you know the other so the "touch and feel" can work till hands are wrecked so use the infrared or stop for a while.
That's about it this system is easy as they go.
*****************
Remote other issue doubt this time is the air dam under front bumper is there to create a vacuum under engine for proper airflow at speed. Otherwise it's jamming air under bumper such that airflow thru grille is all messed up at speed.
I can re-post the temp and pressure chart but this thread is long enough now. It's up top here where I wrote now long ago charging procedures this an exception if real at 105F wait or use some judgement. No joke, when that hot I refuse to work on A/C my bod can't take it with a hot running engine you could bake a cake in those temps - literally!


Tom



johnnydollar79
Novice

Jun 12, 2022, 1:29 PM

Post #12 of 18 (277 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  


In Reply To
When you bring it up to 2000RPM, the pressure should not exceed 300 PSI. Even that is a little on the high side. Most I see will stay under 275 when doing that.


I bled some off and it seems to have fixed the problem. I truly appreciate it! Last question…what vent temp should I expect if ambient is 108 with 12% humidity?


Hammer Time
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Jun 12, 2022, 1:34 PM

Post #13 of 18 (275 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

Again, many variables. Blower speed, recirculated air, how long it's been running.

Doors closed, center vent, blower on high, set to max AC and not parked in the sun it should pull mid 50's after it's run for a while. Some will get colder but that's just better than normal.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Jun 12, 2022, 1:35 PM)


johnnydollar79
Novice

Jun 12, 2022, 1:40 PM

Post #14 of 18 (269 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  


In Reply To
Again, many variables. Blower speed, recirculated air, how long it's been running.

Doors closed, center vent, blower on high, set to max AC and not parked in the sun it should pull mid 50's after it's run for a while. Some will get colder but that's just better than normal.


Max AC, blower on high, highway speeds it got down to 49 degrees at the vent.

Thanks again. I’m done pestering.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 12, 2022, 1:43 PM

Post #15 of 18 (263 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

Glad to hear you got it resolved. Closing this now.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Jun 12, 2022, 3:04 PM

Post #16 of 18 (245 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

One more: The real 105F you see 49F at vent is as good as it's going to get. Glad it's resolved, T


Nacho
User

Jun 15, 2022, 7:00 PM

Post #17 of 18 (207 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

Your Grand Marquis requires 38 ounces (1.08 kg) of R134a. It has a powerful, two-speed condenser/radiator fan. At highway speeds, condenser air-flow increases, but based on that I read, you may have an overcharge condition or a restricted airflow. I don't recall if your GM has a mechanical fan as well (some used to do). I'd start revising the charge to be exactly 38 ounces AFTER vacuum, and take it from there. Make sure the electric fan is working properly and engages in both speeds. If the condition continues, you may also have a clutch plate out of range, or a faulty clutch coil. Do not use refrigerant with sealer or any other additives.
You'll teach them to fly, but they won't fly your flight; you'll teach them to dream, but they won't dream your dreams; you'll teach them to live, but they won't live your life; however, in every flight, in every dream, in every life there always be the print of your lessons taught (Mother Theresa)


Nacho
User

Jun 15, 2022, 7:42 PM

Post #18 of 18 (196 views)
  post locked   Re: 2003 Grand Marquis AC blows warm hwy speeds  

49°F at highway speeds is BARELY acceptable in a Grand Marquis
You'll teach them to fly, but they won't fly your flight; you'll teach them to dream, but they won't dream your dreams; you'll teach them to live, but they won't live your life; however, in every flight, in every dream, in every life there always be the print of your lessons taught (Mother Theresa)






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