P80 fault testing BEHR evaporator... failure

Post by **abscate** » 29 Jul 2020, 09:16

Found the Behr evap from SWMBO bmw I replaces 2-3 summer ago and though I would test it

Symptom ..This car would lose ac performance over three summers due to low charge. I borescoped the evaporator and saw dye and grease stains indicative of a leak.

( skip 12 hours work)

I rigged the evap with a plug and a hose to deliver 3 psi air and submerged it in the bowl of water

I could not find a leak or bubble.

The camera color corrected the evidence away but there is a pronounced. Yellow stain of PAG oil on this.

850oldschool · Post by **850oldschool** » 29 Jul 2020, 10:36

Why only 3 PSI? Why not 100?

Post by **scot850** » 29 Jul 2020, 11:20

What pressure does the system normally run at? I would have thought way higher than 3psi??

It could be that the old oil has congealed into the hole (assuming there is one). Also, you have assumed this is the problem, it may have been a bad seal between the pipes and not the evaporator itself.

Neil.

Post by **abscate** » 29 Jul 2020, 12:51

It’s a TX system so it would run at about 30-60 psi in the evap. When my actual P80 evap went I could see the leak at 3-5 psi easily

The PAG oil and dye stain is clear evidence of evap failure

Upshot. It’s nice to confirm evap failure by finding a hole but false negatives are a possibility using compressed air

yanga001 · Post by **yanga001** » 29 Jul 2020, 12:52

If thats the low pressure side then maybe 20-30 psi would be a better test for checking for air bubbles. It wasnt a catastrophic failure as it kept running, so i believe it is safe to assume that the fault would occur at higher operating pressures. It would probably be difficult to make a 20-30 psi seal so this was the next best test in my opinion.

850oldschool · Post by **850oldschool** » 30 Jul 2020, 17:52

I believe when the engine's not running the high and low sides equalize and the evaporator can have upwards of 100 psi in it. At 100° the PT chart shows 124 PSIG:

https://www.forane.com/export/shared/.c ... -chart.pdf

The PAG oil clearly indicates that there was a leak. But the very slow rate of leakage suggests a hairline crack to me, perhaps it only opened up when the pressure spiked on a really hot day?

Post by **abscate** » 30 Jul 2020, 18:07

I wonder if the replacements are better than the originals. We had our first trouble with Freon loss in 2006, and I looked at the 2013 replacement and it’s pristine

Post by **scot850** » 30 Jul 2020, 19:44

Like everything else out there that is manufactured it could be just a bad one. I've had bad OE parts out of the box so why should these be any different?

Interesting experiment and maybe as suggested it needs a higher pressure to open up the crack to give a slow pressure loss which is not showing at 3psi.

Neil.

850oldschool · Post by **850oldschool** » 30 Jul 2020, 21:54

abscate wrote: ↑30 Jul 2020, 18:07 I wonder if the replacements are better than the originals. We had our first trouble with Freon loss in 2006, and I looked at the 2013 replacement and it’s pristine

We cannot completely rule out the possibility of progress.

Post by **abscate** » 31 Jul 2020, 03:17

850oldschool wrote: ↑30 Jul 2020, 21:54
abscate wrote: ↑30 Jul 2020, 18:07 I wonder if the replacements are better than the originals. We had our first trouble with Freon loss in 2006, and I looked at the 2013 replacement and it’s pristine
We cannot completely rule out the possibility of progress.

I believe they rot out from aluminum corrosion, from the outside in, as a result of humidity that sits on the evaporators. The design of the HVAC system can help with this though. I have two VAG cars from 2002 and 2003 resp on original Evaps and And charge. The Bavarian money waster died at 12 years /150k , P2 going strong at 130k/15 years