T800 inconsistent AC temp

Sometimes the compressor kicks off at 45f, sometimes as low as 28f. Measured at the vent in front of the driver. The evaporator randomly freezes up. I changed the freeze switch not long ago and it hasn't improved. I don't recall if it turns on the pump or if it just shuts it off. The system has been updated to a Sanden compressor and the bunk lines were removed.

As an aside, what's a good vent temp to target? Mid 30s?

allan5oh said:

Sometimes the compressor kicks off at 45f, sometimes as low as 28f. Measured at the vent in front of the driver. The evaporator randomly freezes up. I changed the freeze switch not long ago and it hasn't improved. I don't recall if it turns on the pump or if it just shuts it off. The system has been updated to a Sanden compressor and the bunk lines were removed.



As an aside, what's a good vent temp to target? Mid 30s?

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Anything below 40 is a good day, but I'm in subtropical country.

I'm curious if the probe needs to be relocated. Had to do that on quite a few Navistar units. Next would be air velocity through the core.

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Made some progress, but more questions too.

I completely blocked off the fresh air inlet and that made a huge difference. My guess is when the evaporator starts sweating, it messes with the freeze switch. Good to know. I was consistently getting 37f-39f on and 34f-35f off at the vent to the right of the driver. I watched engine load and went through a good 20 cycles. It is noticeably cooler.

But, then I moved the laser gun. I noticed by pulling it back I could change the reading to 10 degrees warmer. So I grabbed my other gun (different brand) and exact same thing! It seems as though being close or in the air stream lowers the reading.

Then I pulled the vent out, went to the back of the bunk and it was another 10 degrees warmer.

When I have time I'm going to slowly go closer with the freeze switch and see what works. I will report my findings. But it's pretty clear you want as little fresh air as possible.

Colder, not closer

I can't see the inlet air being an issue unless you have a stopped drain, and even then, they just disperse the droplets through the vents and the driver gets rained on. The air flow would have to be extremely low for condensate to have time to freeze to the core.
I ran one yesterday that looked like it had a water hose coming out of the box.

Call me crazy but open your heater valves slightly.

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Replace the low pressure switch. Sounds like it's getting too low(too cold) intermittently. I like to replace the low pressure switches in my personal vehicles with adjustable ones and play around until I find the lowest pressure that won't freeze up. I like 'er cold!

mhuggler said:

Replace the low pressure switch. Sounds like it's getting too low(too cold) intermittently. I like to replace the low pressure switches in my personal vehicles with adjustable ones and play around until I find the lowest pressure that won't freeze up. I like 'er cold!

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It's not a low pressure switch, it's a freeze switch that's in the core and is adjustable.

It hasn't froze up once since I blocked the air inlet.

I had to change the fan. Between that, blocking the intake, and cleaning things it has not froze up once. Obviously there's a lot less water under the truck when I park. I'm actually going to try to make it colder. The vent temp is also much more consistent.