A/C Only Works Sitting Still???

[Sir William]

I've got a 2007 Navigator and the A/C works great when the truck is first started, but once you start moving, it shuts off within a couple of miles. We thought it was stopping when the truck got up to temp, but when sitting still in the mechanic's lot, it ran fine and blew cold for over an hour. But as soon as they took it out onto the road, the compressor cut off in a mile or two and wouldn't come back on until it completely cooled off.

It's not a blend door issue or blower issue, all that still works fine, it's just the compressor kicking out and staying out. There are no codes from the EEC or from the climate control module either.

Just an FYI, we had the whole system repaired last August with new compressor, evaporator, dryer, etc. They also just checked the freon level and it was a tad low, but not much. They did top it up and made no change.

Any ideas of what to look for? The mechanic (not a dealer) is stumped.

Thanks!

 

[riphip]

Sounds like the condenser cooling fan is not working correctly.

 

[JamaicaJoe]

Low Freon pressure? There is a protection switch that cuts out if the low side is too low. Can you put a volt meter on it and go for a drive?

Sent from my SM-T350 using Tapatalk

 

[Brons2]

Get some gauges put on it to see where your pressures are, then if that's ok, check on the cutout switch as Jamaica Joe mentioned.

 

[Hamfisted]

Yeah it kinda sounds like a low pressure condition in the system. Do you have a set of AC gauges you can put on it? What are the low and high pressure readings at idle? And at 2000 RPM ? Or if you pop the hood and run it up to 2000 RPM do you see the compressor kick off ?

 

[07navi]

You need the 2 gauges before you do anything. Not expensive or hard to use. These trucks run close to 30 psi on the low side and 200 on the high side at 70* ambient.

 

[Sir William]

Thanks for all the input guys. The truck is still in the shop....because a black truck with leather interior and no A/C is just not really usable in 90 degree weather.

They're going to look at it again first thing Monday morning and see what the pressures look like at idle & cruising RPM. Also going to check to see if either pressure switch is being tripped then failing to reset itself. Hopefully we'll know something then.

 

[07navi]

Thanks for all the input guys. The truck is still in the shop....because a black truck with leather interior and no A/C is just not really usable in 90 degree weather.

They're going to look at it again first thing Monday morning and see what the pressures look like at idle & cruising RPM. Also going to check to see if either pressure switch is being tripped then failing to reset itself. Hopefully we'll know something then.

Yea, the compressor clutch needs to be on when moving all the time.

 

[Dustin Gebhardt]

My '07 has a bad temperature sensor located in the evaporator/blower box. The sensor shuts off the compressor, theoretically telling the compressor that the evaporator temperature is cold enough and allows for it to de-ice every few minutes. What could be happening in your case is the AC system is inefficient enough during idle that the temperature sensor never reaches the cut off setting, but once you get moving, the AC efficiency jumps and the evaporator temp sensor shuts off the compressor (prematurely, in your case).

I have never seen this issue mentioned elsewhere on the internet. The sensor is fairly cheap, but requires that a large section of the dash be removed, so I've jumpered it until I get ready to tackle that job.