OT Automotive A/C

reomack

Member
I'm generally familiar with auto A/C systems and have been working on them since 65 but I have a very specific question. 2004 Expedition w/5.4 L engine, on hot days and at low speeds (in heavy traffic say) the system will stop cooling. I know that many systems have a pressure sensor on the high side that will disengage the compressor when pressure gets past a preset point to protect system components. Does any one here know whether or not this sensor is particularly prone to failure on 04 Expeditions? Has anyone here had this problem with this particular vehicle and if so how did you handle it. This truck has the dual A/C system and the problem occurs no matter what the system configuration is, given high ambient temps and low engine speeds.
 

The first thang you need to do is recover the refrigerant evacuate and charge with the proper amount. Those dual units will fool you into thinking it has a bad compressor but it's low on refrigerant. Sometimes the front are rear will cool but not both most of the time the rear will cool some but not the front if its low.

If you are experienced as you say you are you can add and feel the lines to confirm system operation. I would be comfortable adding a pound and maybe two and feel that the front evaporator is cool on the suction and discharge side.

That's my free advice YMMV.
 
Your complaint is pretty common with a lot of vehicles, in order to keeps manufacturing costs down they use the smallest condenser coils
possible, which makes any little problem noticeable at slow speeds and high ambient temperatures. You might just have a dirty condenser coil.
If that model has electric radiator fans they might not be moving enough air, or a slightly loose fan belt, if it's not an electric fan. You might have
a small amount of air in the system. You could wire a small indicator lamp in parallel with the electric clutch, so that you can see if the clutch is
being shut off, which would happen if the high pressure sensor is going off on high head pressure. I like Hobo's idea to recover the refrigerant,
and pull a good long, deep vacuum, and then weigh in the correct charge. I don't suspect a low charge, because I am assuming that the cooling
is satisfactory under normal conditions, but you could put your gauges on the system and see if the charge is low. I would clean the coil first,
because it's quick and easy to do, and it could be just that simple on a thirteen year old truck. It sounds like the sensor is working properly, but
I'd have to have gauges on it to be sure.

Jerry
 
Any A/C job requires a visual inspection which I assume you have done. The charge level needs to be verified. I would not guess. Have it recovered to verify charge level as suggested. R 134-A is prone to temperature swings if it's a bit low. If low either they can add dye to the charge to locate the leak or they can do a leak test on it with an electronic leak detector. Your call. The component you refer to is called the A/C pressure transducer.
 
Thanks to all for your erudite inputs. I did add almost 14 oz of 134 while carefully monitoring pressures. System was acting normal after the charge except that it would not cool when ambient was in the 90s. When the problem occurred the front just blew hot air but there was still some cooling from the rear. Next step is to evacuate and recharge. There are no electric fans, the condenser coils are clean. and the accessory belt does not slip. Any more ideas?
 
Don't know if it is applicable on your Expedition but my Freestyle was doing the same thing. Turned out to be a bad scroll compressor control valve. If that is the issue it is a cheap and easy fix.
 
(quoted from post at 07:20:00 02/22/17) Thanks to all for your erudite inputs. I did add almost 14 oz of 134 while carefully monitoring pressures. System was acting normal after the charge except that it would not cool when ambient was in the 90s. When the problem occurred the front just blew hot air but there was still some cooling from the rear. Next step is to evacuate and recharge. There are no electric fans, the condenser coils are clean. and the accessory belt does not slip. Any more ideas?

If the low side was still a little high and the high side a little low add some more. I get spoiled by being able to measure what I take out :D The front always seams to suffer from a low charge sometimes I just go by feel with my hand if its a wham bam thank you mam.
 
Tryin to fix it. At one time in my life I was NIASE certified and I'm still a fair hand with wrenches and I do know how A/C works. It is 13 years old but still has less than 100K on it. so I don't see a junk yard any time in it's near future. But then I'm stubborn and I really like V8 fords (and 8N tractors too).
 
Make sure you change the cabin air filter if so equipped. Had a 2013 Ford edge that the AC would drop off at times. Found that the OEM filter is pretty small and it gets clogged faster than you think.

Best of luck.
 

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