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Learning from bad judgement in auto diagnostics

Tuesday, January 1, 2019 - 09:00
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Now that we knew the compressor and the electrical part of the A/C were operable, we pulled the cold stuff back out and used 150 psi of dry nitrogen to see if we could find a leak that way. We didn’t. So we did another vacuum, injected some dye, and recharged the system. We let it run for a bit and then shut it down to black light it for leaks, but we didn’t find any under the hood. It was time to look deeper.

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This considerable dye drip led us to the leaky evaporator, and while we were there, at the customer’s request we replaced the heater core as well. The orifice tube was in dreadful shape; it took the whole pipe to get this one, but I wanted eyes on the original – it was a good call for sure.

Starting the engine, we put the A/C on again and waited a bit until the evaporator started dripping, and that’s when we saw dye — a LOT of it — in the evaporator drain. Apparently, it would hold vacuum but not pressure. The customer opted for a new heater core and evaporator and we swapped both in-dash heat exchangers out, along with the liquid line, which has the orifice built in. I cut the orifice out of the old line and found that replacing it was a good move. This was the first one of these Tim had done, but he made it happen, and the Jeep has good cold air.

A 2008 Charger

This black Charger turned out to be another electronics adventure and an exercise in discovery and judgment. The complaint was that you had to attempt to start it about 100 times before it’d finally wake up and fire up; that’s the way the owner described it and that’s how I wrote it up and he somehow got it started and brought it the next morning.

Since the scan tool wouldn’t talk and the CAN bus was dead, we poked around in the schematics and determined that the Totally Integrated Power Module (TIPM) might be at fault – interestingly, the owner came up with a used one he got from somewhere and we popped it on there to no avail. Nothing changed at all.

ALLDATA Tech Assist suggested that the Wireless Ignition Node (WIN) might be at fault and said we should check power and ground at that funky little box — this is what most people might call the ignition switch, but it’s a CAN module and apparently wakes up the bus and the other modules, which it was refusing to do. It had power and ground, so we found a rebuilder in San Antonio who would refurbish it for $149 if we’d send the WIN and both fobs, so we did. When the node came back, the Dodge fired right up, but there were other issues — the door locks wouldn’t work unless the WIN (the key) was turned on. With the key on, the lock buttons and the fobs worked fine. Also, the accessory delay problem wasn’t working right – the windows and the radio always kept working even after the door was opened. Oh, and the courtesy lights wouldn’t work unless the key was on. Could the WIN be causing this? For some reason it had no idea the doors were open, and the cluster seems to be the module receiving those inputs.

What surprised us was that fuse 14 was missing, and although fuse 17 also feeds battery power to the cluster, 14 feeds an important part of the cluster as well – and the absence of that feed caused all manner of confusion. Somebody removed that fuse before we ever even saw the car. And that didn’t help either.

As a hail Mary pass, we ran through a check of all the fuses and found fuse 14 missing from the rear PDC (by the battery in the trunk). At that moment we didn’t know it, but when we researched, we found that Fuses 14 and 17 both feed the cluster, and when we installed the requisite 10-amp fuse in position 14 the Dodge was good to go – locks, retained accessory power, courtesy lights, everything. Somebody had planted this bug before we ever saw the car.

A 2008 Nissan Quest

This was another inoperative A/C – we had shoved some juice into this one for the first time in its life about four years ago and it had worked well until about halfway through this past summer. I threw the job at one of my folks who needed to get some A/C troubleshooting worksheets done, and I got involved after she did her preliminary diagnosis.

The Quest owner didn’t report engine overheating, only A/C system failure, and that’s how this one started out.

The Neutronics box had sniffed the juice and given a green light — 100 percent 134a, and when we connected the refrigerant recycler we found we had nearly 100 psi of static pressure, but when we fired up the engine and turned the A/C on, the pressures started climbing and kept going up. The high side went above 400 pounds within 2 minutes and inside, the cooling went away. We noticed that one of the two condenser/radiator fans was running slow and the other one wasn’t running at all, so we shut everything down and did a quick fan electrical test.

This is a fan test I’ve mentioned before, and there are two solid benefits.  First, if the fan fails this test, it’s bad every time. Second, this test can find an extremely intermittent fan problem, and often does, if just one or two of the commutator strips is bad. I devised this method when I was at the Ford dealer and we were having a lot of hard-to-duplicate intermittent fan failures.

There are several ways engineers have wired two-speed fans, and this one seems to be unique to Nissan. These Nissan fans have proprietary relays with two sets of contacts and each fan has four terminals, two of them grounds, and two of them powers for controlling cooling fan speeds and so in order to do our test-light continuity test, we disconnected the condenser/cooling fan that wasn’t running and connected a jumper to one of the two ground terminals in the fan connector (NOT the harness). The other jumper was connected in series with a test light to any positive battery terminal on the motor, and as we turned the fan by hand, the light was winking off more than it was on. That’s a go-no-go fan test that’s always reliable. That one got a replacement fan and a draw-down and recharge with the right refrigerant charge and was once again a comfy ride.

The high side pressure was alarmingly high before the fans were replaced – on a different Nissan, a pickup – we found a bad belt-driven fan clutch causing a similar problem, but it would slip the A/C belt after a few minutes of A/C operation.
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