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AC suddenly quit (in my 4x4 98 Jimmy 4.3) as I was adding Duracool. It had been working, but weakly. I decided to add the Duracool to top it up. Followed directions exactly. When I came to the “turn on engine and AC”, the pressure gauge dropped so I added a bit more until I got the correct pressure, I think 38 lb. I didn't add very much.
It never blew cool again. The clutch isn't turning and I digress here to mention that it is not easy to find where the compressor and the clutch actually is located, if you don't already know.
After reading that the clutch won't engage unless there is a minimum pressure, I got to wondering if it would if I cram some more Duracool in. Then I wondered if I had the system that would engage if the pressure came up, or whether I should try jumpering the low pressure switch first to see if the clutch would actually turn.
There are lots of instructions on how to do this but I'm a step behind. I found the fuse box and located the correct fuses.
Apply voltage directly to clutch connector on the clutch side and ground the other wire.
Checked voltage on the clutch connector. Where is that?
GeorgeLG's post: Work your way backwards from the clutch.
Do you have power at the hot side of the HVAC relay contact?
Do you have power at the hot side of the coil for the HVAC relay?
If you ground the other side of the HVAC relay coil does the compressor energize?
Are you getting a request for AC at the input of the high pressure switch on the back of the compressor? Do you see that signal at the output of the high pressure switch?
My question: Where are these components located and what do they look like?
swartlkk's post: The low pressure cut off is on the passenger side of the engine compartment. The high pressure cutoff is located at the back of the compressor. You could verify that you are hitting the high pressure limit by disconnecting the switch and putting a jumper across the pins in the switch. If that is the case, then there is either insufficient cooling in the condenser, a problem with the filter/dryer causing a restriction, or possibly a clog in the orifice tube causing a restriction.
Not knowing the history of the system, I would recommend that you replace the filter/dryer and at least clean the orifice tube.
My questions: Where exactly on the passenger side of the engine compartment is the low pressure cut off and what does it look like? Also – same questions for the rest of the things mentioned: the high pressure limit switch and the pins to jumper it, the filter/dryer and the orifice tube.
This isn't rocket surgery. I know I can do it if I can only find out where the components are located. I've crawled the 'net for days looking for this info without success.
If I get it wrong, I'm looking at replacing the AC, which is where I am now so I won't be any worse off.
There are two pressure switches that have to be in the correct state for the compressor to turn on. A high pressure switch at the compressor and a low pressure switch at the accumulator. Pressures that are too high or too low will prevent the compressor from starting or cause it to stop. Sometimes the low pressure switch is called a cycling switch because when the compressor is off, the pressure in the system equalizes on both sides of the orifice to the 134a pressure for that refrigerant temperature which is in the middle between the two switch limits. When the compressor turns on the high side pressure climbs and the low side pressure drops until the system equalizes. If the refrigerant is low or the load on the evaporator is low (low ambient temp and/or humidity) then the low side pressure goes below the low side switch limit and the compressor turns off. Then low side pressure starts climbing again to the equalization pressure and then rinse and repeat. The high side switch is rarely triggered and never at startup. Either switch, their wiring or connectors can of course be defective. There can be other reasons for a dead compressor but that's the G2 on pressure switches. Lets rule that out first, starting with the low pressure side.
The low pressure switch is threaded into a port on the accumulator which is at the evaporator inlet in the engine compartment on the passenger side. It looks like this:
The low side switch is threaded onto that 1/4" schrader port. Pull the connector off when the truck is running and there is a call for cooling and short the two contacts in the connector just long enough to see if the compressor clutch engages and then pull the wire or paperclip back out.
An air conditioning system has an optimum level of charge and the only way to attain that level is to either weigh in the nameplate charge level or have a proper set of gauges and thermometers. You then dial in the charge looking at the ambient temp, vent temp and low and high side pressures. Charge levels above or below that level compromise the system performance. With some knowledge and a feel for the process some diy guys can add charge with those parts store cans and get the system to run good enough buts it’s a blind process that can actually be dangerous. An example is an orifice tube blockage and you just keep adding 134a waiting for the low side pressure to hit some target and the high side is getting way too high. Without proper gauges you won’t know that there is a system problem. Too much refrigerant can slug and kill the compressor or cause a high side blow out if the limit switch fails. Point is that blindly adding refrigerant with a small can and a cheap gauge only works if the system is working ok and just needs 134a and you know what you are doing. Also, working with gauges on the high side while necessary for proper AC work is more dangerous because there is 200 psi hot liquid refrigerant at that port when the compressor is running.
Also remember that venting refrigerant to the atmosphere is illegal.
An air conditioning system has an optimum level of charge and the only way to attain that level is to either weigh in the nameplate charge level or have a proper set of gauges and thermometers. You then dial in the charge looking at the ambient temp, vent temp and low and high side pressures. Charge levels above or below that level compromise the system performance. With some knowledge and a feel for the process some diy guys can add charge with those parts store cans and get the system to run good enough buts it’s a blind process that can actually be dangerous. An example is an orifice tube blockage and you just keep adding 134a waiting for the low side pressure to hit some target and the high side is getting way too high. Without proper gauges you won’t know that there is a system problem. Too much refrigerant can slug and kill the compressor or cause a high side blow out if the limit switch fails. Point is that blindly adding refrigerant with a small can and a cheap gauge only works if the system is working ok and just needs 134a and you know what you are doing. Also, working with gauges on the high side while necessary for proper AC work is more dangerous because there is 200 psi hot liquid refrigerant at that port when the compressor is running.
Also remember that venting refrigerant to the atmosphere is illegal.
George
I want to second what George wrote.
Looking back what happened to my AC is likely what George described; I added refrigerant hoping that would fix the problem. Instead it turned out the problem was that the compressor vanes were disintegrating which clogged the expansion orifice. When decided to replace everything, I found that the system was over-pressurized, not empty due to a leak like I had thought! (Sorry atmosphere for venting the R-134a. I didn't mean to do that!)
So, if it turns out you need to replace your whole system, I have a writeup on my build thread you might look at. It wasn't too hard to do except for the hassle of getting out the condenser in front of the radiator. That was super annoying. I was only able to keep the evaporator. As for the proper tools, I was able to borrow them for free from a local Autozone including a vacuum pump.
More HVAC systems are overcharged rather than undercharged, in residential systems at least. It is a common mistake made by even many professionals that more gas is the universal cure. This is probably more true in automotive because there is more leaking but still not the best assumption. A proper set of gauges and thermometers with some knowledge prevents that issue. Just like saying just charge to a "cold can of beer".
Appreciate your concern and I'm aware of the issues mentioned. I'm going by the fact that the AC was previously working. I haven't done anything yet as the air here is opaque with wildfire smoke. Rain is forecast in a couple days and I'll get to it when the air is somewhat washed.
DURACOOL® products are replacements for R134a and R12. They are not only non-ozone depleting, but are also non-global warming. It contains no CFC's, HFC's or HCFC's.
Appreciate your concern and I'm aware of the issues mentioned. I'm going by the fact that the AC was previously working. I haven't done anything yet as the air here is opaque with wildfire smoke. Rain is forecast in a couple days and I'll get to it when the air is somewhat washed.
DURACOOL® products are replacements for R134a and R12. They are not only non-ozone depleting, but are also non-global warming. It contains no CFC's, HFC's or HCFC's.
I have no experience with these products so I have no idea if they are illegal to vent into the atmosphere and I don't know Canadian law so I'll stay out of that subject.
I also don't know what the procedures are for existing systems, if this new product can be mixed with existing 134a or if a changeout procedure is required. The usual problem is incompatible oils which can cause a hell of a mess when mixed. You can get a slime that plugs up the orifice tube as a minimum. I only bring this up because there may be another variable to your problem. I will leave the research on switching over up to you and will advise you on issues not related to this, or IOW the things I have experience with. Also, the charging pressure charts will probably be different than the generic 134a charts.
07-26-2021, 02:09 PM
AC again
