|
|
|
So I've got two bricks with almost the same problem - both have either faulty low pressure switches or the connector plug/wiring is the problem. Sometimes the A/C works and sometime it doesn't. Fiddling with the connector (removing/replacing) or bending the wires at the connector will sometimes get the A/C going. Sometimes. Usually works best when first starting up, not when it's warm/hot. And when it's working, the switch/connector/wiring problem usually will cause the A/C system to shut off/on several times a minute, causing the engine to hesitate momentarily as the A/C clutch cycles on/off.
Questions: I assume replacing the switch requires evacuating the system and recharge? Any tips on repairing/replacing the connector and wires? I've tried some electric clean spray and dielectric grease, but that wasn't enough.
Thx in advance BB's!
|
|
-
|
|
|
I really think your problem is just coincidence with you moving the low pressure switch since it seems that both vehicles are doing it. I have rarely seen one of those go bad but I guess it can happen. More than anything I think your cars are just low on freon. The type that the 92's use tends to leak out a bit faster than the older R-12 did. When they get low they will cycle the pump every 10 or 15 seconds, depending on how low they are. The newer vehicles have overcome this problem with better seals and hoses. Not sure if yours has a sight glass near the low pressure switch area but if so look to see if there are a lot of bubbles when it is actually running. If so then have it serviced or do it yourself. Just my opinion and I am usually wrong. Max
|
|
-
|
|
|
Hi there,
I sure hope you are right and I can say you have about a 60/40 chance it can be the switch.
I would like to add some insight to this systems "quirks" for lack of a better term.
This system strictly works on a pressure difference like any other refrigeration cycle but it can only monitor pressure. It knows nothing of temperature of the cabin as there is no thermostat. You are your own thermostat as you turn the fan control for more or less capacity up to its maximum transfer of heat limits. All of that was decided by engineering the size of both coils and their fans.
The amount of liquid refrigerant was also set on this design limit. It has to be precise, within a few ounces or there is not room on one side or too much on the other for the gas to function in balance. This charge was reach as a compromise to do away with a more complicated and expensive expansion device, let alone "A" cabin thermostat to give you something to twist on to make them work faster. (:)
Overall you cannot say this system is bad. On the contrary, this is the same type of system used in about 90% of domestic non-commercial refrigerators. They are called "capillary tube" where as this one is called an "orifice tube" expansion device. They are both create a pressure drop and set flow limit between the halves.
They are built to do a specific job in a specific cooler market or a tropical climate, for instance, affects these fixed units. A tropical fan clutch, maybe other things?
Different markets have their own compromises.
Thermal expansion devices do not have access to changing the load capacity with a reserve of refrigerant, built-in. It's held in items called high side receivers. It's a slight overfill reserve. By using a thermally control "variable meter pin or a "run wild" restriction, to control evaporator flooding back to the compressor, larger droplets are allowed in to boil off. The orifice is shorter and larger but pressure activated.
That is why you see the large aluminum can that has that pressure switch. It's an accumulator or catcher to boil off liquid droplets before it can get to the compressor.
The switch is your safety guard against flood back and your sole heart that keeps the evaporator from frosting or freezing up. Frost stops air flow and cooling.
That's "A" complaint that you mentioned about starting out early and it not working well later. Frost over can cause the short cycling. Pay attention to amount of air flow at different fan speeds during trips as humidity changes over terrains. Florida or the East coast have their days!
The switch can get out in two ways. Overall range can move around or the set "dead band" can move between wider or closer together. I suspect the overall can be moved as there is a screw between the terminal prongs. Turning it ever so slightly might help but again I only suspect it's a factory adjustment of range for climate humidity. If the differential is messed up, the switch is done.
Another thing, if you are twisting the harness or flipping the switch inside, remember that there is a time delay relay in circuit with the on off switch in the cabin. It takes about five seconds plus for the compressor to start.
Remember, it's a compromise built system or was an under funded one to pay for the bigger components to make up for 134's loss of efficiency.
The AC Delco system type design was down sized from the USA, used on bigger engines, now put on a four banger. It's not your old man's Bu..sick anymore!
FYI
The older systems were just slightly under sized. Sweden didn't need A/C or ice in most cases. Their engineers bought things from a "handy dandy catalog" to get them through those early years.
It Helps to explain the rubber bushings "hanging on" to everything else out there! Plus those split and shimmed crankshaft adjustment pulley.... plain Ugly story with that one!
Dealers had them installed, by other shops, in the North America of the 70's. In most cases, the expansion devices were not "tuned" to sense properly. I know, I got one and I learned to tweaked them in a little better.
Good luck!
I'll watch for your update to see how it went.
Phil
|
|
-
|
|
|
there's a schraeder valve on the ports, so just unscrew to old sw. and that's it. good luck, chuck.
|
|
-
|
|
|
Thanks for the quick reply Chuck - just to be clear when I unscrew the switch the schraeder valve will keep the system sealed and pressurized with no Freon loss? Do I need to do this very quickly; is there a few turns for leakage while the switch is being backed out before the valves seals?
|
|
-
|
|
|
OK, answered my own question, slight 17mm wrench action, then it spun off easy, just a quick spst and a drop of foamy oil was all. Gonna order a new one, I think that's my culprit.
|
|
-
|
|
|
Thank you everyone for your replies and input, a lot of good info and ideas there duly noted for future reference. I did replace the switch on both cars at about $30 each, super easy to do. So for they are both blowing cold a/c and no more -chugging-. But we are just entering the warm season here in FL, so time will tell. I'm aware about the temperamental refrigerant charge requirements, so if it can't keep up w/ the warm weather, it will be sent to my mechanic who can do that part as I don't have the tools/time/knowledge to handle the freon stuff. P.S. machine man in the past the 92 had a plugged orifice problem that occurred after a evap or cond replacement, some debris must have broken loose somehow.
|
|
-
|
|
|
Hi again,
Good to hear that the switch may have been the problem.
If you think about it, there is a lot of responsibility put on that switch to maintain good working conditions of being cold enough but not too cold.
Not only does it have to snap on and off correctly, it has to carry the current of the magnetic clutch.
Knowing what happens to contacts over time of several arcings it doesn't surprise me that they eventually develop an issue of losing range and popping right on the dot. I have often wondered if I should add a power relay into the circuit to help shuttle that issue onto a bigger package, if that is what shortens their accuracy?
Anyway, thats why I gave you the 60/40 odds on it being a problem. At least one of the engineers thought to make it easy to change out by having the schrader underneath the switch.
As far as the debri in the system can be a in depth subject. Something caught in the orifice, is one of the biggest bug-a-boos with any expansion device but cap tubes, seldom clear easily.
Cleanliness has to be when it comes to pulling the sweat off the brow and having them working properly.
At least the Engineer gods had enough experience to leave in screens and a desiccant package help deter the problems that cannot always be avoided.
Unfortunately in this system, most of these devices are "after" the expansion device, not before it.
IMO a major flaw in its design.
Things can be seen they used to save money by reducing numbers of components on inventory and assembly cost but moisture and leaks have always been an enemy. This system has the least joints of most units short of having sweat fittings and no rubber hoses. I noticed on my '92 that there are no schrader valves on the back of the compressor.
In some realms, this happens to save weight added to the car. To me, this might be giving into an extreme priority at the cost of reliability and serviceability.
The next step would be to do away with an engine driven compressor and make the whole system into one solid apparatus or package.
I'm rather fond of ideas that use heat to transfer heat energy. Like absorption designs, rapid air exchangers or electronically controlled conductive device designs. These must be on a more grand scale to get five or more tons of cooling. Passive comes with limits and today's consumers, of whom want things instantly, well... kills all of that. But within time, I'm sure there is a way to evolve systems and environments.
Back to the system that has minor issues, IMHO the desiccant filters work best with the "condensed liquid" and not with gas droplets of the low side.
If you have moisture, the worst thing by the way, in a system is that the water vapor can be more readily absorbed as a liquid than it will be if in a frozen molecule state, into a "cold" dry desiccant rated in only a few "drops" of capacity.
An ice crystal will form within an expansion device and block it just as nicely a ball type check valve. Luckily, it does melt during the failure or off time and moves on again. Intermittent cooling then occurs until it gets removed.
All particles of debris, be it dirt, metal, oil impurities or water has more of a chance to be born within the compressors components or allowed in during a change out or recharge!
Just about any foreign particle will be supported by velocity of flight on the low side or just after the compressor. But, it's the largest ones, that collect in a liquid will flow easier around in the system.
A river can push more solids than a cloud. All of that River stands in front of this orifice but protection is provided by one ply of fine mesh screen. Just appears to be a lot to ask? There by another weakness IMHO.
The pressure switch, on a "no leak please" balanced system, along with impurities spells out "frustration to diagnose."
So smile it is staying clean and leak free. Use it as much as you can and enjoy it while it works!
Phil
|
|
-
|
|
|
Well, here we are again, replaced both (92 and 93) low pressure switches last year(along with other AC work as per usual on a brick AC system), and now the 92 LP switch appears to be not working, again. Easy fix to switch them out to check, sure enough when I put the 93 over to the 92 the AC started working again. But 1-2 years on these parts is frustrating. Maybe buy a case or any ideas on what's up on this?
|
|
-
|
|
|
Hi,
I haven’t had that many failures with the low side pressure switch but then I don’t use my A/C very much to begin with. I try to stay out of any days of summer heat!
This is why I’m lucky to own (if you don’t count taxes and ever rising essential service fees, even when your not there) two coastal homes to hide between.
One is way north in California until it rains too much as I might get webbed feet. It’s then, I slide down the coast halfway in between Mother Nature’s cycles.
I”m Not a snow bird, as I don’t like that stuff either!
The earlier systems let the Expansion valve do the proper pressure setting of the evaporators temperature to prevent icing up of the fins. Plus a cabin thermostat was an added cost that got away from with an orifice tube device. You can tell this system is not my favorite system for all kinds of reasons because of what they took out. Less expensive, is the bottom line, words here!
This is my estimation and this is based somewhat on the physical size of the body of that switch!
Most switches should have to earn a certification to handle at least several thousands of cycles to be an automotive switch or any switch for that matter.
It’s unknown what the current rating is because it’s not put on the switch. So that’s a clue in itself!
The contacts in that switch, are probably being subjected too much current load. Not the greatest design to work such a crucial function!
I cannot vouch for problems with the snap action, but most of the time, heat affects the mechanics?
Food for thought on both sides of the following:
Since you are have this much of a reoccurrence, you might be wiser to putting in a cube relay to be powered by that pressure switch that gets its power from the console in the cabin.
They are not the strongest switch either, as I got a used car cheaper because of that issue.
This will let the relay handle the load by using another supply source over to the relay.
The magnetic coils can and do draw lot of current, especially, if they are “Working On” short circuiting themselves internally.
You might want to do a comparison test, between those two cars you have, if you have a ampere meter. Check them over a time period of several minutes for draw changes.
Trouble is, they are fairly reliable and a long shot!
The coil may be getting hotter than it should, but there is no way to measure that since it’s under a clutch and pulley.
Could be a bad clutch engagement issue too?
Does it make a squeak or chirp? You only want it to have a solid click?
About .015- 020 clearance is plenty of spacing for releasing. Check with a feeler gauge.
More than this and it might be slipping some while driving?
I have gotten away with resurfacing the faces and shimming back closer, but in today’s world it’s all about R&R, of which, means shims again anyway.
If things measure out equal, then again, consider an auxiliary relay to power up the coil!
Phil
|
|
|
|
|
