"Short" in the Air Conditioning System

[Woody]

My Air Conditioning stopped last summer... Or, more accurately, wasn't working when I turned it on for the first time last summer. I took it to my neighborhood shop who checked the coolant and said it was perfect, they checked the fuses and relays, they even "hot-wired" the compressor which promptly turned on and began pushing cold air. their final determination? A short in the system somewhere which would take 1-4 hours to locate at $75/hour, not including parts and labor to repair if required. Since I normally bike to work in the summer, I used this as additional motivation and left it be.

 

Come this summer, my father discovered that I have no A/C and insisted upon taking it to his friend's shop to have it repaired for me... And here's where it gets fun:

 

We stopped by after hours to grab my car and there was indeed A/C, but the engine seemed to be running rough and there was a hissing noise coming from under the hood... I opened it to look around and the noise stopped. I got back in, shifted to drive and the engine promptly died. Tried again, the hissing was gone and it chugged forward. Long story short, it turned out the mechanic had run a wire from the compressor relay to ground, so that it would run whenever the A/C was on. This threw off the RPMs, and I'm assuming the hiss was a release valve from too much pressure in the system. I was... In a word... Pissed. Once I removed the wire, all of the problems went away, but of course so did the A/C. My father insisted on bringing the car back to that mechanic so that he could fix what he had done. The mechanic then claimed that the car's computer was shot and would cost $600 for a new one. However, since they seldom died, he could probably find one from a junk yard for less. I refused.

 

Now, I don't have a degree in automotive engineering, but I have friends who, one way or another, have fried their car's computers. And every single time the failure was, in a word, spectacular. Never did a computer stop just a single system from running, it was always a full-out crash which brought down everything from the ability to unlock doors to failure to shift out of Park. Could I be wrong here? Perhaps... but even if I am, I think that I would rather pay Ford or Lincoln for a new computer and installation than this particular mechanic. I've scoured this message board for other options and explanations and the closest I've found is either the temperature control head unit in the dashboard or a temperature sensor. So, on my lunch break I drove to the nearest junk yard who had one in stock and they allowed me to plug in a new control unit... Still no A/C. So... It could be a sensor, but at this point I've schedule an appointment for tomorrow morning at my local Lincoln dealership. Any last-minute suggestions would be appreciated, otherwise I'll let you know what they determine... (All of the posts here I've found have had a surprising lack of closure.)

[Woody]

Just got my call back from the Lincoln Dealership... I need a simple little Air Conditioning Evaporator Discharge Air Temperature Sensor, Part #19C734 which runs about $17.49.

 

The bad news? It's going to take about 7 hours of labor to remove my entire dashboard, at $145/hour. Total quote? $1,039 for parts and labor.

 

Needless to say, I'm looking into other options, including making the repair myself. For those who wish to give it a shot, a relatively easy to follow step-by-step guide is provided HERE.

[Woody]

As an update... I had the sensor replaced and the A/C... kinda worked, but not great. And within a few days, the blower went out. Since that was new and supposedly had a warranty, I had it brought back to my father's friend's shop. I explained that new blowers don't do this and chances are, as I had originally said, there was nothing wrong with the blower. I suggested the Blower motor resistor might be the most likely culprit and after four days of ordering the wrong part over and over again, they finally swapped it out.

 

Unfortunately, now it's kinda cold outside... There is definitely cool air blowing, but I question if it's COLD. At this point however, I'm wondering if there is still enough refrigerant in the system? There was one point where, while the compressor was still "hotwired" that I heard a pop and a puff of smoke shot out of my engine compartment. What that could be, I'm not certain as everything else seems to work. So... My guess at this point is that there's some safety valve that blew when too much pressure built up in the system. I'm sure I can get through the winter, so I may just wait to see what's up next summer!

[Woody]

We've had warmer days on and off... I defintely don't have COLD air conditioning and there is a severe amount of hissing/wheezing noise coming out of my dashboard when the A/C is cycling on and off... A friend told me it sounded like his grandmother with Emphysema was trapped inside my dashboard... I'll likely wait until spring to have this looked at again.

Edited October 25, 2011 by Woody

[Woody]

Update: The wheezing is still there and I'm not sure what it's from, but after recharging the coolant, I've actually got air conditioning... Sometimes. All of a sudden, the system is acting up again and randomly, the blower will simply stop working. The compressor is still running and if I'm at highway speed, I can open the back windows a crack to "suck" cold air out of the vents and into the cabin... So now I'm trying to figure out what to replace next or, more likely, again.

[FusionDiffusion]

Running the wire like that so the compressor runs all the time was such a hack job. That mechanic must know next to nothing about modern A/C systems with temperature sensors and electronically controlled clutches. I'm afraid you were right because wiring the compressor to be on all the time can overpressure a system. There is a pressure relief valve on the compressor, so when you heard a hissing noise and saw a cloud that was probably all the refrigerant blowing out. Understandably the system was now low on refrigerant, so even after you replaced the bad temp sensor the system wasn't going to cool properly until the charge was properly adjusted.

 

Now your A/C should not have a wheezing sound, but I might have an idea what it is. You A/C system uses a thermostatic expansion valve (TXV) to regulate the flow of refrigerant through the evaporator core in the dash. However, when that moron wired the clutch to be on all the time and over-pressurized the system, the TXV had to hold back all that pressure so it's likely it was damaged during that event. So I would recommend TXV replacement to try to get rid of the wheezing. Luckily it doesn't require removal of the dash (it comes out from the engine compartment), but it does require the A/C system to be evacuated, opened up, and recharged again afterwards.

 

The intermittent blower operation could be a number of things. It could be a bad blower motor itself, or anything from a bad relay, blower switch, resistor, or a ground. You would have to get in there and troubleshoot all the parts with a DMM and hope you can find the problem. Last time I ran into that problem the blower motor was bad (the spring holding one of the bush contacts broke, so when you went over bumps the motor would cut in and out and you could smell ozone from the arcing). When the blower goes out, does turning the fan speed control (like setting it on high) do anything?