Heater Core or AC Evaporator Issues?

[LakeBob]

I was experiencing leaking from the bottom of the AC/Heater core box attached to the firewall of the coach.  

See below, the rust that has developed  on the firewall where the AC/Heat box attaches.

I noticed a drip after a days travel last fall when we had to use chassis heat one morning. 

 

Heater/AC evap box removed: 

 

 

I pulled the heater core, plugged one side and applied pressure, 25 psig, and no leaks were evident. The core released pressure when I removed the air.  I was expecting to see something in the area below.  The only rusty area on the entire core. 

I increased pressure to 35 psig and experienced the same result. 

What kind of pressures does this system operate at during normal conditions?   I wondering where else this leak could be coming from?

Should I increase pressure and test again?

The AC seems to drain well, I notice the drips on the pavement when that system is running, so I doubt this rust is caused from the AC evaporating.  

From the date code this appears to be the original heater core.  Someone has been in here before; new hardware and broken box flanges were found. 

Thanks!!

Edited May 3 by LakeBob

[jacwjames]

Check your manual, there should be a section on the pressure to charge the AC system. 

Not sure what the heater core sees for pressure.

Edited May 3 by jacwjames

[Ivan K]

Heater core pressure should not exceed the engine radiator cap rating. You would likely know it it was coolant leaking. Leaky evaporator would be nasty oily. Condensation is a nature of beast.

[LakeBob]

Thanks guys, I'm confident the AC evaporator is good, the AC works well and holds pressue, just had it serviced last September.  

Im just surprised I didnt see an obvious leak with the heater core.   I may be a little low on test pressure, I'll check the cap and see if there's any info. 

 

[Ivan K]

The cap will be half or less of your test pressure unless stuck and you would be likely having other leaks at that point 

[cbr046]

Radiator cap is 14 psi?  Whatever it is, that's the pressure throughout the system.  If it survived 35 psi it's a good heater core.

If it "leaks" make sure your AC compressor isn't engaged and the evaporator isn't forming condensation.  If the AC compressor is on the low pressure tube (the larger diameter one) will be cold and may be sweating.  Easier to touch the tube at the front vs opening the rear bedroom hatch and looking at the AC clutch.

- bob

[Rikadoo]

WOW! First things first hats off to you Bob, i have torn into removing units like that an there not for the faint of heart. Next i would like to know what color was the fluid on the ground that you saw? Was it the same as your engine coolant? Most radiator shops after pressurizing them dunk them in a tank of water as a crack in the copper tubing is really difficult to find, now that said perhaps it might be a benifit to see if you still have a radiator shop that you can have test the core. From personel experiance there mostly previlant in small towns anymore mostly due to local epa crackdown.

[LakeBob]

1 hour ago, Rikadoo said:

WOW! First things first hats off to you Bob, i have torn into removing units like that an there not for the faint of heart. Next i would like to know what color was the fluid on the ground that you saw? Was it the same as your engine coolant? Most radiator shops after pressurizing them dunk them in a tank of water as a crack in the copper tubing is really difficult to find, now that said perhaps it might be a benifit to see if you still have a radiator shop that you can have test the core. From personel experiance there mostly previlant in small towns anymore mostly due to local epa crackdown.

Thanks, it was a fairly easy job on my rig.  There's one screw on the upper left that is a problem, have to do my touch, will be fun getting that one back in.  

Yes, a radiator shop might be able to determine if there's a leak, it may be very small and I cant hear it. I'll try some soapy water today.  I'm hoping it is good as the first replacement I found was $525....ouch. 

[LakeBob]

Test Time: Rigged up a water test for the core. Tested at 30 psig for 5 minutes each end.  Needed to alternate submerged ends to test the entire core. 

No bubbles.....

 

 

Frustrated that I didn't find a leak, as I just don't see how the leak I observed occurred without the core leaking.   The only thing I did not mention is I observed the leak 4 months ago when arriving at our winter  spot and we had to use the heat that morning.   We did not use the chassis heat the entire 1800 miles home. I'm wondering is some debris or scale has plugged a small hole in the heater core? 

There is a mixer valve just outside the Heat/AC box, perhaps it was leaking?   I'll take a closer look at this.  

Regarding Assembly:  What type of seal would you recommend for sealing the box to the firewall.  I was thinking of a butyl tape?  OR Closed cell foam tape?

Replacement Heater Core 042-00044:  I did find a replacement core for $175 on Ebay.  Will talk to some other manufacturers and the local radiator shop tomorrow to see what other options are out there. 

 

 

[LakeBob]

So I've dealt with this stuff for many years, usually carefully removing and replacing, and I've never had to apply new.  this was applied to the outside of the HVAC box, sealing the AC and heater core lines. 

Is this just a thick strip of butyl rubber?  Pick up at any auto parts store?   

Thanks! 

 

[Ivan K]

AC insulation tape, Prestite tape, used on exposed line and valves. Available on Amazon amongst others.

[DBRV.0]

LakeBob: it certainly seems that you have thoroughly tested that heater core, proving that is is good.  I suggest looking for some other source. 

Like you mentioned, perhaps a valve is leaking or a connection to the core such as a hose clamp that was not tight?  And speaking of hoses, could a connecting hose have a crack?  The system is closed, so you should be able to pressurize at less than the radiator cap (mine is stamped as 16 psi), and use soapy water to check hoses and fittings.

As cbr06 suggested, if the AC compressor was running, its evaporator might be condensing moisture.

I haven't checked the area on my Dynasty (same as yours), but could there have been rain water on those days?

If all else fails, maybe consider keeping your heater housing open/unattached and running the system to observe.  Matter of fact, after considering the options, this might be the easiest test.

- Jeff

[cbr046]

I just discovered my house (stick & brick) AC was caked in ice.  If your evaporator did that, and it does happen, it would drip for hours after shutting down.  That is, of course, if you used the AC on a humid day. 

- bob

[LakeBob]

On 5/5/2024 at 4:43 PM, Ivan K said:

AC insulation tape, Prestite tape, used on exposed line and valves. Available on Amazon amongst others.

Thanks, I found several types of "refrigerant tape".  

[LakeBob]

I took the core to a radiator repair shop, where they explained that pressure testing can push calcium or other debris into tiny holes, falsely indicating the core is in good condition. They perform vacuum tests on everything; if the core fails to hold a vacuum, then there's a problem. I hope to hear back from them today and will update on their findings. This approach seems logical for detecting small leaks.

(The above was a rewrite of my original post by the sites AI engine. It popped up just before I posted and asked if I wanted to use this feature.  It did enhance the communication a bit.     Its an interesting world we live in!)