Brain storming

[Robyn]

Just thinking about the issue with the PMD failure.
So many companies have come up with a load of ideas to help reduce the heat factor via heat sinks and such.
What about mounting the PMD on an aluminum heat sink that is fastened to the AC accumulator. Hmmm now there is nice cold spot that will suck all that extra heat out.
Just my mind wandering again.
Now I know not all rigs have AC but a lot do.
There are other places in the engine bay that have access to the suction line of the ac and could easily accomodate a heat sink being fastened.

?????????????
Robyn

[john8662]

Lightning? Thunder?

Maybe...

Not a bad idea, I don't think you can run them "too cool". I would be worried about moisture though, in the form of condensation, it's electronic afterall.

But, the biggest problem, it's still in the engine bay, which is a heat haven. The only solution there is a cowl induction hood, fixes that.

I like the thinkin' tho!

J

[Shikaroka]

It would only help when the A/C is running (which may be the best time anyways). But, I'd say it would also affect the effiencey of the A/C.

For illustration of my claim:
On my VW there is a small insulator that goes around the expansion valve on the firewall. I had taken if off for something and I could tell a difference in the cooling ablity of the A/C. When I put it back, it cooled better again. I was surprised at how a little heat in the lines could make a big difference.

[DmaxMaverick]

It would only help when the A/C is running (which may be the best time anyways). But, I'd say it would also affect the effiencey of the A/C.

For illustration of my claim:
On my VW there is a small insulator that goes around the expansion valve on the firewall. I had taken if off for something and I could tell a difference in the cooling ablity of the A/C. When I put it back, it cooled better again. I was surprised at how a little heat in the lines could make a big difference.

The expansion valve was effected for a different reason. The valve adjusts A/C orifice size according to freon pressure, evap temp, and ambient temp. If you remove an insulating cover, it will throw off the function of the valve. Insulation on an accumulator/receiver/dryer is only to increase the efficiency (prevent heat soak) and reduce condensation.

I think John is right. Condensation could be an issue, along with temp extreme swings. I don't think what little heat the FSD generates would degrade the A/C performance to a noticeable degree, but the condensation could kill the driver. All the FSD needs is a method to dump its heat, which is easy if done correctly.

[Shikaroka]

AH! I see.

[jilaroo2]

I built my PMD in the front fender opening on a black alluminum heatsink ($6 on ebay)that just fits that opening. Not only does it look good but it doesn't even get warm at all.

[moondoggie]

Good Day!

It was initially thought that FSD/PMD failures were due to the fuel solenoid drive transistors getting too hot. Then folks started finding that tightening loose hex nuts on these transistors fixed some of the dead or intermittent FSD/PMD's. Some other folks found additionally that the transistors had cold/broken solder joints at their PCB pads. I don't recall anyone ever actually removing FSD/PMD drive transistors, testing them, & finding them defective (if you have factual knowledge to the contrary, PLEASE correct me here).

It was proposed that both the loose hex nuts & cold/broken solder joints were due not to overheating drive transistors, but the extrememly large temperature swings a FSD/PMD is exposed to in either the factory on-the-IP location or the heatsink-on-the-intake location favored when folks began addressing this issue.

For my rigs I'm betting the under-hood temperature extremes are the main issue, NOT the transistors themselves. I base this on pretty close to zero hard factual information, & a little electronics intuition I may still possess.

Back to the subject of this topic. Mounting the FSD/PMD on the A/C accumulator might not be a bad way to go. It might be less affected by under-hood temps, especially if the FSD/PMD is mounted toward the outside of the vehicle. Even with the A/C not running, the accumulator is a pretty big heat sink, regardless of whether it's at ambient temperature or 35F with the A/C on.

Difficulties to consider: 1) IMHO it will be very hard to get a good low thermal resistance connection between the FSD/PMD & the accumulator. The accumulator has a pretty rough surface, relative to the surface required to get good thermal transfer. 2) Also, it's round, adding another potential difficulty to both its mount & the previously-mentioned thermal resistance issue. 3) The condensation DEFINITELY has to be addressed. 4) If wide ambient temperature swings are indeed at least a part of the FSD/PMD failure issue, this location will possibly add to this problem - instead of the temperature swings of the on-the-IP or heatsink-on-the-intake locations, whenever the A/C is on the FSD/PMD mounting surface will go sub-ambient.

I'm leaving my FSD/PMD on my JK extension harness, right in front of the driver-side battery. I have no idea if this will help the lifetime of this part or not, but that's how I'm gonna handle this expensive gamble.

Blessings!

[rjwest]

inside the cab, where the AC air blows on it, small hole in air box, small duct to computer fan that blows on PMD heat sink.. Remove duct for winter, And easy to replace PMD

[john8662]

I built my PMD in the front fender opening on a black alluminum heatsink ($6 on ebay)that just fits that opening. Not only does it look good but it doesn't even get warm at all.

Let's see it, take a picture! You can host it in the Photo Album for the rest of us to see :)

[jilaroo2]

Pics posted in album.

[rfuntime]

Jillaroo2......nice pics. I placed mine closer to the center, behind the licence plate bracket. Helps to keep it out of the elements. Sometimes I check to see how hot it is....usually air temp or slightly higher. Works good!! Paul