Town Car AC Pressure Readings

[HighwayStar]

Does anyone have a Town Car specific source on what the AC manifold gauge pressure readings should be for the Town Car? I just got done measuring mine. By generic charts this thing seems overcharged, but maybe this is normal range for the Town Car. 2006 Signiture L if that matters.

 

[Action]

Pressures are variable based on ambient temperature.

I should have them from a 2006 Lincoln Navigator shop manual if that helps.

Action

 

[HighwayStar]

Yes, that would be a helpful data-point. I do have ambient temperature and humidity readings to go with the manifold gauge pressures.
However, I realized I had the valves screwed shut rather than open, and I am now of the hypothisis that the system is slightly undercharged but having a range from a comperable system would be helpful.

 

[Action]

Pressures given do not factor humidity.
Pressures expressed as PSI
Temperatures expressed in f
This is shown in the shop manual as a graph as far as temperatures.

Low side pressures
70 degrees 28 to 45 psi
75 degrees 28 to 49 psi
80 degrees 29 to 55 psi
85 degrees 30 to 60 psi

High side pressures
70 degrees 110 to 179 psi
75 degrees 120 to 180 psi
80 degrees 130 to 195 psi
85 degrees 150 to 215 psi

The graph goes to 100 however not sure you will see much higher than 85 this time of year.

In my experience, I have never gotten the low side below 35 psi. However, this is in Phoenix and the temps are typically over 85 when I am doing this kind of work. My personal goal is to fill and get the low side below 40. At 40 psi the evaporator is putting out at near 40 and by the time it comes out of the vent register the air temp is likely just under 50. If the ambient is 35 to 45 degrees higher, that just below 50 degrees feels like ice.

Action

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[HighwayStar]

Many thanks Action.

Yes it was about 75 when I tested yesterday, but its good to have a range since I will be messing with this for another week or so. I certainly hope it does not go over 85 before I get this fixed.

When the compressor kicks off low side is down to 20 psi, high side is up to 150 psi. When the compressor kicks back on low side is up to 60 psi and high side is around 125.
My understanding is the reading should be taken when the compressor is running, so 20 psi and 150. That sounds like it is a bit low on refrigerant.
Have you seen 60 psi on the low side when the compressor is not running? I want to rule out orifice tube/expansion valve (whatever the Town Car has).

Also worth noting that the compressor cycles about every 12 seconds.

 

[Action]

(Some of my best AC work was done in triple digit ambient temps)

How cold is the air coming out of the register?

I would agree with you, I think the system is a little low. Or the orfice tube has some restriction.
Because the low is is low and the high side is a little low too.
That is an indication of not enough refigerant or the orfice tube is restricted. ( I believe all Town Cars had orifice tube to the end of production)
The shorter clutch cycle time supports this.

So let's back up. What happened to the AC system prior to yesterday?

Action

 

[HighwayStar]

(Some of my best AC work was done in triple digit ambient temps)

How cold is the air coming out of the register?

I would agree with you, I think the system is a little low. Or the orfice tube has some restriction.
Because the low is is low and the high side is a little low too.
That is an indication of not enough refigerant or the orfice tube is restricted. ( I believe all Town Cars had orifice tube to the end of production)
The shorter clutch cycle time supports this.

So let's back up. What happened to the AC system prior to yesterday?

Action

Vent temp is about 68 degrees with outdoor temp at 80 driving down the road and stopped at a light.
AC has been weak for at least a year, last summer I had it out when it was really hot and it was definitely not cooling well. Hard to say if its gotten worse since I did not measure anything last year.
Not sure what happened to it prior to Sept 2021, when I bought it.

 

[Action]

System is loosing refrigerant.
Just may be not a big leak.
Assuming everything is original, adding a few ounces maybe with some oil or leak detection might be prudent.

Any idea of system capacity?

Action

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[Action]

Oh the orifice tube. It is a restriction in the system that also has a screen.
Any debris in the system will be caught in that screen.
There is generally one place in the system that will create debris.
That is the compressor.

Every time the system is opened, pull the orifice tube. It will tell a story.
Generally you will want to replace it because it is so cheap. They used to be less than ten bucks. With inflation not sure any more.

Action

 

[HighwayStar]

System is loosing refrigerant.
Just may be not a big leak.
Assuming everything is original, adding a few ounces maybe with some oil or leak detection might be prudent.

Any idea of system capacity?

Action

23 oz. R-134a is the stated capacity. This is an L model so it might differ slightly from the other Town Cars.
I figured the same, not sure how long it has taken to loose this much refrigerant, but I'm tempted to add UV dye and a small amount of refrigerant to bring pressures up to normal.

 

[Action]

The system is still working. Adding the dye and a small amuont of R134a should be a good plan.
It won't take much to fill. And you do not want to over fill.

Is the L an extended body?

Action

 

[Action]

Never mind. The evaporator is all the same for all models.

Action

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[HighwayStar]

The system is still working. Adding the dye and a small amuont of R134a should be a good plan.
It won't take much to fill. And you do not want to over fill.

Is the L an extended body?

Action

Yes that was my thought. A small amount with some dye. If nothing else it is a cheap step that may fix the issue and show where its leaking.
L is the long wheelbase. I have read conflicting things about how, if at all, the HVAC system differs for these. There does seem to be a different compressor.

 

[HighwayStar]

Well, I tried adding some AC tonight. I don't think it was a large amount (based on can weight, etc) but whatever I did raised the pressure with the compressor running to about 165 on the high side and about 30 on the low side. Compressor will now run continuously for close to a minute instead of short cycling.
Yet...vent temperatures are unchanged. I want to take a drive tomorrow and verify this under identical conditions, but I can certainly say it is not "right" even if it is slightly better.

 

[Pantherswithoutcoils]

Well, I tried adding some AC tonight. I don't think it was a large amount (based on can weight, etc) but whatever I did raised the pressure with the compressor running to about 165 on the high side and about 30 on the low side. Compressor will now run continuously for close to a minute instead of short cycling.
Yet...vent temperatures are unchanged. I want to take a drive tomorrow and verify this under identical conditions, but I can certainly say it is not "right" even if it is slightly better.

The short cycles is the biggest indicator that there is not enough refrigerant in the system. The compressor has a low pressure shut off switch that keeps the compressor from running without enough refrigerant. I went through this last summer….I would add an aresol can I could pick up from the parts store, and my compressor would stay on longer, and even blow slightly cool air, but it would never last long. I finally took it to a shop and had them evacuate and refill the system, been blowing snow balls ever since

 

[V35A]

I’ve found that many leaks are at the valves on the service ports. Sometimes loosening them 1/2 turn and retightening will make them seat better.
Not relevant to this problem but it’s good to keep the condenser clean of any debris.

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[Action]

I’ve found that many leaks are at the valves on the service ports. Sometimes loosening them 1/2 turn and retightening will make them seat better.

Which is why the caps should be on the port at all times when the system is not being serviced. Keeps debris out of the port.
And when serviceing the system, remove the valve and inspect the seal. If good, use refer oil as a lube on the service valve seal before reinstalling.

Action