Automotive Air Conditioning Information Forum

Doesn't matter where you add the dye/oil. It's all going to be mixed up in 10 seconds once you run the system.

More importantly, did you get all the flush out of the system? Any flushing agent left behind will break down your oil and cause a compressor failure.

kenlou wrote: Tue Jul 15, 2025 8:26 am I would add that to the high side in other words, inlet side of the evaporator, correct?

Since there's currently no charge, I'd add to the most convenient place. Even if you are suspecting/checking for a leak in the evaporator.

More importantly, did you get all the flush out of the system? Any flushing agent left behind will break down your oil and cause a compressor failure.

I blew air in the evaporator for 20 minutes off and on and got nothing but air out.

I agree with Tim. Adding dye to the TXV side or the suction side of the evaporator, I don't believe it makes any difference.

Backing up to your previous post:
Just the opposite...the outlet side of the evaporator is the other larger diameter line. The thinner high-pressure line is the liquid line that feeds refrigerant to the TXV and then to the evaporator, and it runs from the R/D to the TXV/evap.

John, you’ve got me confused here. The thinner high pressure liquid line on my truck runs from the condenser to the smaller line on the evaporator which is the inlet, correct?
So, if I flushed the evaporator through the larger diameter evaporator line (this line comes from the R/D on my truck) I am “back-flushing” the evaporator. Is this the preferred way of flushing the evaporator?

I did use the complete gallon of flush and it was clear when I was finished flushing.
Each time the flushing canister was empty, I continued blowing air into the evaporator for a few seconds.

When I completed the flushing, I used my air gun to blow into the evaporator for a good 20 minutes and when finished, I got nothing but air out of that line. I am using a pancake compressor with an additional 10 gal tank and a
NEPIKE 3 Stage Air Compressor Drying System, Particulate & Coalescing Filters, Auto Drain Air Compressor Water Separator System Filter


In hindsight, I wish I would have kept track of how much flush actually came out of the evaporator as I was flushing it.

kenlou wrote: Wed Jul 16, 2025 9:40 am John, you’ve got me confused here. The thinner high pressure liquid line on my truck runs from the condenser to the smaller line on the evaporator which is the inlet, correct?

Yes.

kenlou wrote: Wed Jul 16, 2025 9:40 am So, if I flushed the evaporator through the larger diameter evaporator line (this line comes from the R/D on my truck) I am “back-flushing” the evaporator. Is this the preferred way of flushing the evaporator?

I think the system on your truck has an accumulator, not a R/D. If so, then what you're describing is correct. To be absolutely thorough, you can also flush the evaporator in both directions. IMHO, there's nothing wrong with that.