AC problems on my 2014 Pete 384.

[corneileous]

Well, it’s not my truck, it’s my bosses truck but being that our mechanics can’t figure it out, I thought I’d come over here and see what you guys might say.

But AnyWho, the AC works great when you’re sitting still, but if you’re going above a certain RPM down the highway, the AC will get warm and then get cold and then get warm again and then sometimes it’ll stay cold for a while and then it’ll stay warm for a while and the only thing that I’ve been able to discover on my own is that when I go to check the low side AC pressure with my little gauge I keep in the truck, the low pressure is low enough to the point where the low pressure switch cuts off the compressor and the one time when the truck was in the shop and they had their other hoses hooked to it that shows the high side and the low side, the high side has almost enough pressure to where the high-pressure switch will shut it off from having too much pressure… and yes, like I said, at the same time, the low side will have low enough pressure to where the low pressure switch kicks off the compressor and the only way that I found to make it not be that bad was to unplug the high-pressure switch and jump it with a piece of wire so that I can put a little bit more refrigerant in the system to the point just below where the pressure relief valve on the compressor releases some of the refrigerant.

There is one other thing too… With the fact that my engine fan stays on all the time, would that might have something to do with that?

 

[corneileous]

Anybody?? Well, over the weekend, they replaced the expansion valve and uh, that wasn't it.

 

[crash68]

Hopefully they pulled a good vacuum, replaced the desiccant, and weighed in the charge with fresh refrigerant after replacing the expansion valve.
If it was bad valves in the compressor the pressures won't be correct. The actual problem would be masked if extra refrigerant is added to compensate for pressure or temperature.

 

[corneileous]

Hopefully they pulled a good vacuum, replaced the desiccant, and weighed in the charge with fresh refrigerant after replacing the expansion valve.
If it was bad valves in the compressor the pressures won't be correct. The actual problem would be masked if extra refrigerant is added to compensate for pressure or temperature.

I'm really not sure what all they did but what do you mean when you say if it was bad valves in the compressor, the pressures not being correct?

To my knowledge, they didn't even mess with the compressor because all they did was just replace the expansion valve that's right there on the firewall where the two AC lines go inside the cab, which, on the bottom of it is where the two pressure switches thread onto.

But OK, before they even replaced the expansion valve, what would generally cause an air conditioning system to be so high on the high-pressure side to where it's shutting the compressor off due to high pressure, but also being so greatly low on the low pressure side to where the low pressure switch is shutting the compressor off? I'm not saying these two things are happening simultaneously, I'm saying that if the low pressure switch is the one turning the compressor off, then, when you go to add refrigerant to the system just using one of those refilling cans that only goes in through the low pressure port and then you raise the pressure up enough to where now the high pressure switch is the one shutting the compressor off. In other words, if the low pressure side is down to 20 pounds of pressure, only the low pressure switch is what's turning the compressor off and when you go to recharge the system through the low pressure report, you can only get the low pressure side up to about 33, 34 psi before the high-pressure switch starts to shut the compressor off.

 

[crash68]

before they even replaced the expansion valve, what would generally cause an air conditioning system to be so high on the high-pressure side to where it's shutting the compressor off due to high pressure, but also being so greatly low on the low pressure side to where the low pressure switch is shutting the compressor off?

What could cause this would be a restriction in the refrigeration system, hence why they tried changing the expansion valve.
If someone added refrigerant before the expansion valve replacement to resolve a low pressure issue, that could cause the eventual high pressure problems.
Reason why I mentioned the valves in the compressor, it's possible the internal valve(s) were getting weak causing symptoms that would appear to be low on refrigerant.
Aside from a bad expansion valve, other causes of pressures like what was happening would be a restriction, or non-condensables.
Since the expansion valve has been replaced, weighing in a fresh refrigerant charge should give a competent technician who knows refrigerant systems a fresh slate to troubleshoot further problems, like bad compressor valves.