MusicLover

Have a 2004 Lariat 5.4 super crew that has an unusual a/c problem. It will work fine when the ambient temperature is "cool", like below 75 or so. It will not work when the outside temperature is "hot". (Houston area) When I say work, I am talking about the a/c clutch engaging. When engaged everything works fine. Blows very cold air. No problems with blower or vent gates. Climate Control Unit functions normally when changing temperature setting. (fan blows stronger as temp is lowered and cuts back when raised)

The first time I get in the truck on cool mornings the a/c works fine. And then later in the day, as the temperature warms up, it will not work. I took it to a shop and they replaced the clutch relay and it worked for about 3 days. I took it to a different shop in Austin and they diagnosed the problem as definitely electrical, not mechanical or refrigerant. Clutch relay was still good. It was late in the afternoon so they didn't have time to check it in depth so I came home (2.5 hour drive) without a/c in 95 degree weather, not fun at all.

So I guess I am interested in knowing what would cause the clutch not to engage when the outside temperature gets hot, but works fine in the cool of the morning. I do not have the tools to really check things out, just wanting to know what to expect when I take it to the shop again.

Thanks for any help.

gpojunk

I have a similar problem with a 2016 XLT. Although the A/C does work intermittently on hot days.


[Ed: Sorry, I wrote this before I realized I had dropped into the 2004-2008 area. My problem may be completely different in a 2016 truck.]


In mine the prob seems to be with the Ambient Air Temperature sensor. On a random basis, but mostly when the air temp is above about 75 deg, the air temp reading errors out and throws a Poo73 code, and just reads -39 0r -40 deg on the display. The A/C shuts down. At highway speeds the air temp reading will frequently be displayed as 50 deg, and the A/C will be cool but not cold.


I've had the Ambient Air Temp Sensor replaced a couple times under warranty already, but the problem continues on an intermittent basis. I'm wondering whether there is a harness problem. The other possibility is a PCM problem I guess, but I hate to think that before figuring out something simple....

SCORGE

Ask them to check the clutch Gap.
Improper gap can cause the compressor to not function properly.
How many miles? Maybe something blocking flow of refrigerant.
Hard to say

BadFish523

Do you have automatic climate control or manual?

digitaltrucker

Did they evacuate and recharge based on the under the hood specs for r134a? What you are describing is classic for a low system.

MusicLover

Thank you for the comments.

I thought about the ambient temperature sensor but it is right on showing the correct temperature so it seems to be working ok.

I have tapped on the clutch with the handle of a screwdriver trying to get it to engage when the a/c was turned on with no success. I have not actually measured the gap so I will do that if I can find my tool. As for the refrigerant, when the compressor is running there seems to be no problem with the refrigerant at all. The temperature of the air coming out of the vents is cold and changing the temp up and down responds as it should with the gates functioning properly to adjust the temperature of the air coming out of the vents.

The truck has 163,000 miles and has been maintained by the service manual schedule at the Ford dealership where I bought it new.

digitaltrucker

Have you checked the low pressure switch? If equipped?

MusicLover

I do have the automatic climate control and it was replaced about 7 years ago.

They did not evacuate and recharge the system as far as I know. I figured that would be the next thing I would have done after I replace the low pressure switch. I have already replaced the high pressure switch and have the low pressure switch and new elctrical plug adaptor from the Ford parts store at the dealership.

BadFish523

Check and clean the connections on the back of the climate control?

MusicLover

I might mention that right now the biggest problem I am having is that it is working fine. Until it quits working again, I don't want to mess with it so that when I do replace the low pressure switch I will know if it helped or not.