"CORRECTION" 2003 5.4L Expedition. Are these A/C pressures acceptable? I may have overcharged

[Jersey Jim]

CORRECTION: Mistakenly wrote "275" but high-side pressure at 2100 rpm is 375 PSI

In attempt to locate an A/C problem earlier in the week, which I soon after found to be a corroded A/C clutch-coil connector, I may have overcharged by adding a 12 oz, can of R134A. Here's what I measured just now on first hot day all week:

Ambient: 92F
High side/Low side equalized pressure: 108 PSI
Equalize time: 20 minutes after shutting off hot engine (75% in 10 minutes)

Engine Idling Pressures: 50/240 PSI

Engine raised to Highway speeds (2100 rpm): 30 psi/375 PSI


This 5.4L has rear A/C evaporator, and system capacity states 54 ounces R134A.

I witnessed no clutch cycling while Idling. All blowers on high, max cold, and all open windows.

I was by myself, so too noisy at 2100 rpm to hear clutch cycle. If it did, was prob from high-pressure switch.

Do these pressures look a little too high, or acceptable? I added Freon earlier in week when rainy and cooler, cuz low side was sucking down to 20 psi or below. I did not want it to cut out.

Also, does anyone know the pressure "opening" pressures for the low and high switches?

 

[stamp11127]

The idle pressures are a little too high for me but within range of the r134a charts.

Static pressure chart for r134a and r12:
https://www.google.com/search?clien...0.0.......0.khAyadtc7Eg=#imgrc=ZsAyvE83lRuPUM:

Only worry about clutch cycling if the system is measuring evap temps, then it will cycle. The basic systems run until over pressured or under pressured.

How is the cooling at idle?

 

[Jersey Jim]

stamp... thank you for reply..... Please read my correction in my original post. Performance seems to be very good. I never got this A/C cycling problem corrected since I bought this vehicle in summer of 2016, so don't know what is factory performance. However, at idle, air blows in the 40's. At driving speeds with fans on high, I get mid to low 40's with an outside ambient of 87F.

Clutch never cycles off at Idle or at highway speeds, which is what I was hoping for. That tells me the high-pressure cut-out switch can handle 375 psi without interrupting. Is this typical pressure rating for a high switch? Rolling down the highway at same 2000 rpm's, I was only assuming pressure would be the same 375 as sitting hot in driveway an hour earlier. Or does air movement at 60 mph bring that high pressure down some?

While driving/testing, digital thermometer on floor, near evap return and out of the way of any vent breezes, the vehicle got down to 67F with full sunny day, and dash outside temp of 87. I was very comfortable, and pleased with performance, but worried about high pressures or frequent safety cycling.

 

[Jersey Jim]

I also ordered an OBDII link from Amazon, in hopes I could use Forscan to monitor high/low pressure switches, evaporator temperatures, and clutch-coil relay output. Is this product (link below) capable of doing this? I read some positive posts about this ELM327 interface and the Forscan software, so added this to my infrequently used auto tools. I got a set of manifold gauges from Harbor Freight this week for only $48 with a 20% off coupon!! Was on sale for 59.99 from normally $74. How can anyone NOT buy this for their arsenal, especially at that price?

https://www.amazon.com/gp/product/B006NZTZLQ/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

If the link doen't work, I copied the Amazon description:

ScanTool 426101 OBDLink MX Bluetooth: Professional OBD-II Scan Tool for Android & Windows

I also got a pc Bluetooth dongle to receive the wireless data. I hope I'm on the right track.

 

[BRIANGEE]

Good luck with those Harbor Freight gauges. I had to swap them out three different times at the local store for different reasons. I ended up getting some better gauges off of amazon.com.

 

[Big Brian]

I would not be playing around with Harbor Freight gauges

Especially on the high side of the system

 

[johnboneske]

To me those pressures are high. Low pressure should be 50 to 60 psi, and high side should be 275 to 300. You are overcharged... Although your low side seems low and your high side seems high. Weird... Does your Expy have a cabin air filter? If so,it needs changed!

 

[Jersey Jim]

To me those pressures are high. Low pressure should be 50 to 60 psi, and high side should be 275 to 300. You are overcharged... Although your low side seems low and your high side seems high. Weird... Does your Expy have a cabin air filter? If so,it needs changed!

Does the lower than low, and higher than high, indicate some sort of restriction in the lines? I see on the firewall, probably right against the evaporator, is a Thermostatic Expansion Valve (TXV). A block of aluminum with what appears as a disc on top. A few days ago I didn't even know what one was. It appears to have what I think is my low-pressure cycling switch threaded into it. I have been reading about those sticking open or closed. Does that mean I don't have an inline screened restriction orifice (for lack of the proper term). Does a system have one or the other, or both?

Is there a standard rpm that pressures are taken at, other than idle? I used 2000 or so because that's where I cruise at while towing the boat, always with overdrive disabled, and a few hundred rpms higher than with overdrive.

The high pressure safety never cut out my compressor during highway driving or anytime else during the test. So I guess I never reached critical pressures, whatever that is.

 

[stamp11127]

High side is too high at 375. You start heading into green spray territory around 425+ psi on the high side. That is the main reason you don't bypass the high side switch.

I would "reclaim" 6oz and see what the pressures are then. Also make sure the condenser is clean - hose it off with a garden hose. And that the fan is covered by the fan shroud. You want the maximum amount of airflow though the condenser.

Usually when the txv screws up it is all the way closed or all the open.

They will use a txv or an orifice tube or both. Which ever is cheaper for the production run.

 

[Jersey Jim]

Ok Stamp, I made some pressure adjustments, and these are the new readings. Hopefully you and others can tell me if they are more typical/acceptable. Granted it wasn't as hot as yesterday, but today I took readings inside my barn where the heat was building and engine was on more than an hour. I did notice that when I observed low-side readings at 2000 rpm, the pressure drops within a minute, about 9 psi when I cut both blowers down to the lowest setting. 30 psi on full air movement, down to 20 or 21 psi when both blowers on lowest air flow. That was interesting to observe, yet understandable when I got to think about it.

Ambient: 83-85F
All doors open and both front and rear blowers on High, Max cold (recirculate), no clutch cycling.

2000 RPM: 30psi/225 psi. Evaporator outlet (dash vents) 22F colder than floor-area inlet, no clutch cycling.

Idle 800 RPM: 46 psi/185 psi. Evaporator outlet (dash vents) 18F colder than floor-area inlet, no clutch cycling.


I wish I had discovered the corroded clutch-coil connector Before altering the charge. So what do you make of pressures? Looks right about where it should be, for this temperature anyway. These charts never tell you at what rpm you should have these readings!