Another AC Post

[mwr1203]

Brand new Truck. Less than 500 miles. Today it sat all day in the hot TX sun. Went to go out around 4 PM and got nothing but hot air from the AC. Started the truck, and pretty much right away the E-fans ramped up, but the engine wasn't even warmed up. Opened up all the windows turned AC on auto 68 degrees and nothing but hot air. About 15 minutes down the road AC kicked in blowing cold. Worked fine after that. E-fans back to normal. Anybody???

[thewhitestallion]

that is weird. the only times I have had my fans kick on to near 100% is when I disconnected the battery to put in my level and HID lights I then reconnected the battery and when I started the truck those fans were moving some serious air!

[mwr1203]

AC had a low charge right off the lot. Didn't realize it right away. A buddy of mine is an AC mechanic. He said the low pressure suction line first of all should be sweating quite a bit in this TX humidity. It wasn't at all. He put some gauges on it and found the low side at 28 PSI @ 95 outside air temp. He said it should be more like 32-35 PSI. He added some Freon and it feels like AC now and the line is sweating. This was a one time incident. It sits in the hot sun everyday at work. I come out start it up and turn the AC on no problems. Today like I said was different.

[foo.c]

The lower the PSI on the low pressure side, the colder the air temp. At some point it can get so cold the coils freeze over and air can't blow through, but if you just jumped in and started it that can't have been the issue.

 

It kind of reminds me of my old '03 where it would randomly start blowing heat until you restarted it.

[mwr1203]

28 PSI was to low. Line wasn't even cold or sweating.

[Spurshot]

Here's a pressure chart. Ambient temps at the condenser really swing the correct operating pressures. The condenser temps should be measured with air blowing over it like you are driving.

 

I've encountered the issue where the AC would not work initially, then after the engine bay warms up, it works. This is because the static system pressure is too low to trip the low side pressure switch which allows the compressor clutch to energize and engage. When the system warms up from the engine heat, the static system pressure comes up.

 

I was on a trip from L.A. to northern Idaho and meandering thru Washington's wine country when my 2008 AC quit working in Yakima. It was 105F. I had noticed it was getting intermittent and pulled into a NAPA. I bought one can of Freon, a can tap, and bummed a paper clip. I went out, opened the hood, jumped the low side switch with the paper clip, and filled the can into the system. Total time: ~ 10 mins. My wife thought I was McGiver. The system has worked fine ever since that happened 4 years ago. I got a little luck on the amount of charge. I could have over filled it. But I took an educated guess that it had to be very low for it not to trip the low side switch when ambient temps were that hot. Turned out the pressures were right in the middle of the normal ranges when I checked it after returning home.