Automotive Air Conditioning Information Forum

Hi everyone,

I'm hoping to get some insights and validate my understanding regarding my Ford Excursion's A/C system. I'm running into some challenges optimizing its performance, especially with the aftermarket parallel flow condenser.

My Setup:

• Vehicle: Ford Excursion V10
  • A/C System: Fixed Orifice Tube (front) and Rear TXV
  • Recent Work: System overhauled ~1 year ago due to non-functional rear A/C. All components were flushed and replaced.
  • Condenser: Replaced OEM piccolo tube condenser with an aftermarket parallel flow unit.

The Problem:
When I initially recharged the system, I used the factory specification (68 oz). While it performed well at around 80°F, it struggled significantly at temperatures above 90°F.

I've since learned that parallel flow condensers typically require a reduced refrigerant charge compared to OEM piccolo tube units. This leads me to believe I was overcharged, and that I can no longer rely on the factory weight for charging.

My Approach & Current Issues:
I've been attempting to charge the system using differential temperature testing, but it feels inefficient, and I'm not sure I'm doing it correctly. It currently has 60 oz of refrigerant, where the factory calls for 68.

Condenser Temperatures:

• • Readings are often close (e.g., 154°F in, 153°F out) unless RPMs are high enough for the fan clutch to engage.
  • When the fan is engaged, I see about a 15°F difference. I've read that the ideal drop should be between 20-50°F.

Center Duct Temp:
Regardless of operation (idle, raised RPM), it is consistently greater than 30°F below ambient.

Recent Pressures (at ~114°F ambient):

• o Low Side: 50-55 psi
  o High Side: 295-300 psi

Duct Temps at Idle:

• o Blower Low: 34°F
  o Blower High: 45-60°F (depending on idle duration)

My Questions & Suspicions:
1. Is this the best performance I can expect given my setup? I understand I have a few factors working against me:

• o A shared A/C system (front and rear)
  o A large, black SUV in a desert climate
  o An aftermarket parallel flow condenser

2. What is the recommended charging method for a system with a parallel flow condenser when the factory charge weight is no longer applicable? Are there more efficient ways to perform differential testing, or other methods I should consider?

3. Regarding the condenser temperature drop: Is a 15°F drop too low, and does it indicate an issue (e.g., still overcharged, airflow problem, or normal for this setup)?

4. I currently have approximately 60 oz of refrigerant in the system (vs. 68 oz factory spec). Should I aim for even less given the parallel flow condenser?

Any advice, shared experiences, or diagnostic tips would be greatly appreciated!
Thanks in advance.

What year is your vehicle, and how many miles has it logged? Have you replaced the fan clutch lately?

It has been mentioned on this Forum in the past that older-style condensers have about the same capacity as the parallel-flow type. If that theory holds true, it would make the system undercharged by about 12 percent as you currently have it.

As you mentioned, a system with front and rear A/C will have to work much harder to cool a large, dark-color vehicle on a very hot day in the Desert Southwest, especially with both the front and rear A/C turned on.

The engine at a slightly raised idle speed with the compressor engaged doesn't reveal much. Suggest recharging it to factory specs, increase the engine speed to ~1,800 RPM, and re-test pressures and center vent temperatures—first with the front A/C turned on, and then with both the front and rear A/C turned on. Those results probably will be the best they're going to get with a new fan clutch and full factory refrigerant charge at ~114°F ambient.

Thanks for the response, John.

To answer your questions:

Year/Miles: It's a 2003 Excursion with approximately 180,000 miles.
Fan Clutch: The fan clutch is indeed new and was replaced as part of a larger engine overhaul – refreshing the A/C system was a "bonus" while everything was already out.
RE: the condenser capacity theory, I'll definitely keep that in mind. It does challenge my assumption that the parallel flow would require less charge.

Edit: My apologies, I realized I didn't specify what I meant by 'raised RPM' in my first post. For clarity, those observations were taken between 1,700 and 2,000 RPMs.

My reasoning for focusing on idle speed was that the (new) fan clutch moves a significant amount of additional air at higher RPMs compared to idle. This stark difference in airflow (and change in temps at the in/out line) at idle leads me to suspect the A/C's efficiency drops considerably without that forced air. This seems to coincide with why some Excursion owners install auxiliary electric fans. Additionally, this observation makes me wonder if a variable flow orifice tube (the current one is a Ford OEM fixed type) might be a worthwhile consideration to help improve idle performance, but I'm trying my best to NOT Frankenstein / customize the system.

[Q] Based on these observations - should my readings & measurements be taken with the RPMs at ~1,800?

Admittedly, regarding the suggestion to return to a full factory charge, I have some hesitation, primarily due to a previous overcharge condition - potentially attributed to excessive oil in the system, outlined below.

When I initially overhauled the A/C, I believe I inadvertently overcharged the system with oil. I diligently measured and added oil per component, but in my haste, I added 4 (more) oz to the accumulator after realizing the original one was defective (it passed vacuum testing, but the connection failed under pressure w/ refrigerant). I, unfortunately, didn't account for what oil might have already circulated or what was retained in the faulty accumulator. This, combined with the factory refrigerant recharge, consistently caused the system to hit the pressure cut-off switch and resulted in poor performance at idle or at speed in broad daylight.

This time around, I installed an Agility brand condenser (to account for the unknown level of oil in the existing condenser), and assumed it might be "better." However, the row count seemed similar to the previous UAC unit. I thoroughly flushed the lines, replaced the drier, and added the appropriate amount of oil for the system (14 oz).

My reluctance to perform an additional full factory charge stems from the recent cost of R134a, the amount needed to perform a full charge, and my inability to precisely recover a specific amount in the event it results in an overcharge.

All this to say, I found this forum as a valuable resource through a Google search, and I'm hoping these details can serve as useful data points for others - while understanding that this is a product of my own doing

Thanks again for your input and suggestions, John! It's much appreciated.