My A/C cycles the compressor A LOT. Like a dozen times in a 4 minute data gathering run. FORSCAN shows the EVAP temp dropping to 1*C, the compressor cutting out, the EVAP temp warming to 4*-5*C then the compressor starting back up. The A/C request etc. look normal so thinks me. I THINK I'm slightly under charged, but then it could also be....

1) Lack of airflow over the coil (dirty, something blocking the coil)
2) Bad EVAP temp sensor

It's not too expensive to have the system evacuated and recharged on a recovery machine that will measure what comes out and that would answer the under charge question.
I'm wondering how hard it is to test the EVAP TEMP SENSOR to see if it's acting right. Or just trust FORSCAN?

 

Best thing to do is connect manual gauges and see what they're reading. The gauges will tell you if the system is low on refrigerant or not and you can take it from there.

 

There's nothing to indicate the sensor is faulty.

What you're dealing with is a lack of sufficient data to evaluate. The gauges, as already suggested, would provide details about what is happening in the system. You really need to see what the high side of the system is doing. If you can figure out the PID for the AC pressure transducer, that could also help instead of the gauges. You may need BOTH for a complete evaluation.

Also, clean your condenser and check the operation of the cooling fans. If there is insufficient or no airflow through the condenser, the system will short-cycle due to excessive high side pressure and will mimic the behavior of an undercharged system.

 

I’ll be checking the gauges again today when I have a teenager home to hold the rpm at 1500 or so. I can’t manage to see them from the operating position and it doesn’t act up at idle. At idle this morning, 78* ambient temp it was at 35/190 compressor not cycling. At 1500 rpm it does. I’ll look for that PID in FORScan too.

 

Yeah that sounds like it's a bit low on charge.

 

Those numbers are almost dead center in the "normal" section of the graphs for the conditions described.

 

Ok. I got a helper and did a check. 88* ambient Max A/C , fan on high, 1,500 rpm. On startup the low side goes to 40psi and the high side climbs to 400. This takes about 30-45 seconds. After that they settle in at about 30/225 and all is well for 6-8 minutes with no cycling and good cold outlet temperatures. Then the cycling begins.
Here is a link to a video of the gauges while it’s wearing out the clutch.

https://drive.google.com/file/d/1jz-...w?usp=drivesdk

Sure has me curious.

 

Abnormal.
Within normal bounds.
... and how is it cooling when this happens?

 

It’s getting SUPER cold then swinging warm. Overall center vent temperature is mid 50s. The compressor is cycling so much that the clutch stinks. And based on the FORScan data it’s being told to cycle vs a slipping clutch. The evap temp goes to 1*C just before it starts a cycle. I compared it to our ‘14 Flex and noticed that it’s evap temp goes to 4-7*C and stays put. The Flex’s pressures look more “normal” too at 42/275. After a test run ( I took not all that many bugs and junk off of the condenser) the truck was 35/275 at idle in the same environment as the Flex. So...that said. I talked to my tire shop guy (best you can find for A/C work in small rural towns) and we're going to do the evac/recharge and make sure it's REALLY properly charged. He has the machine that will do the job ez pz and it won't cost much. If it still does the cycling thing at other than idle I get to try and pick a good shop to work on the beast.

 

Is the condenser cooling fan running before it hits the 40/400 pressure?

 

It's hard to read the gauges but to me it looks like the low side is dropping to 15 not 30. If that's the case your charge is low.

 

OK, Funny (ironic). Had the system evacuated / recharged to 29oz. Now it's 55* out and I can't tell if anything changed.

 

Ah, just roll down your windows... or wait until August...

 

...or he could install a Redneck air conditioning system.

 

I see absolutely no fault with that ^^^ system!

Well apart from it obscuring the right side mirror---pure perfection otherwise.