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Discussion Starter #1
So my A/C stopped working after a year of not using the truck as a daily (I only drove it randomly). I got married, bought a house, etc. so needless to say, dailying the truck became financially appealing... but I've driven 7 months without A/C. Initially, I had a slight leak in one of the valves on the lines, so I had the system evacuated and I replaced the valve. I had the system refilled by my friend who is a residential A/C tech and we noticed the compressor try to come on and then shut off. He suggested it might be the pressure switch in the evaporator. I tried jumping that, no dice, compressor wouldn't start. So, I ran a wire from the compressor to the battery and got it to start, but the A/C will not blow cold. I know my lines are charged and they held vacuum for over an hour before being charged, thus I know there are no leaks. Could I have a stuck expansion valve? What else should I consider? This is on a 96 Tacoma Xcab, rwd.
 

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Mambeau / Admin
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A/C isn't something i know much about, but ...

It seems to me the pressure switch theory might be correct. If the A/C was turned off while you were charging the system I can't figure out how the compressor would try to activate unless the pressure switch was somehow triggering it.

Here (attached) is the 1996 A/C circuit diagram.
 

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Mambeau / Admin
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Here (attached) is the 1995.5 / 1996 A/C pressure switch test procedure.
 

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Discussion Starter #5
Really hard to say without installing gauges on it to monitor low and high side pressures
I've actually got gauges. I need to test them out again and see where the pressures are sitting.

A/C isn't something i know much about, but ...

It seems to me the pressure switch theory might be correct. If the A/C was turned off while you were charging the system I can't figure out how the compressor would try to activate unless the pressure switch was somehow triggering it.

Here (attached) is the 1996 A/C circuit diagram.
I had the system set to on when I was charging it actually. The compressor initially grabbed and was spinning, then the clutch let go. I always wonder where you get all this awesome info about Tacomas lol, I'll look at the PDFs you uploaded. Thanks Enola!
 

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I've actually got gauges. I need to test them out again and see where the pressures are sitting.
I had the system set to on when I was charging it actually. The compressor initially grabbed and was spinning, then the clutch let go.

I attached the EWD which has a System Outline of A/C operation.
It Contains good info


I'm curious as to why you don't have power going to your compressor to engage the magnetic clutch.
Either a fuse, an open circuit between the amplifier and compressor... or the amplifier isn't seeing what it needs to see in order to send out the needed voltage.
But... being that you directed voltage from the battery to the clutch and forced the compressor to engage/spin... and yet still didn't cool is quite odd.
so either the compressor isn't pumping, the system has insufficient refrigerant, too much refrigerant, or a restriction.
Still comes back to being easier to diagnose with a gauge set
 

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Discussion Starter #8
I attached the EWD which has a System Outline of A/C operation.
It Contains good info


I'm curious as to why you don't have power going to your compressor to engage the magnetic clutch.
Either a fuse, an open circuit between the amplifier and compressor... or the amplifier isn't seeing what it needs to see in order to send out the needed voltage.
But... being that you directed voltage from the battery to the clutch and forced the compressor to engage/spin... and yet still didn't cool is quite odd.
so either the compressor isn't pumping, the system has insufficient refrigerant, too much refrigerant, or a restriction.
Still comes back to being easier to diagnose with a gauge set
Thanks for the data. I'll read those over and see if I can figure something out!
 

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So my A/C stopped working after a year of not using the truck as a daily (I only drove it randomly). I got married, bought a house, etc. so needless to say, dailying the truck became financially appealing... but I've driven 7 months without A/C. Initially, I had a slight leak in one of the valves on the lines, so I had the system evacuated and I replaced the valve. I had the system refilled by my friend who is a residential A/C tech and we noticed the compressor try to come on and then shut off. He suggested it might be the pressure switch in the evaporator. I tried jumping that, no dice, compressor wouldn't start. So, I ran a wire from the compressor to the battery and got it to start, but the A/C will not blow cold. I know my lines are charged and they held vacuum for over an hour before being charged, thus I know there are no leaks. Could I have a stuck expansion valve? What else should I consider? This is on a 96 Tacoma Xcab, rwd.
I have my EPA 608 & 609. Based on what you've tried, I'm guessing another leak. If the compressor is turning (with power directly to it like you did) and the fan is blowing, it should blow cold air if it's still charged. R-134a is a relatively small molecule compared to R-12 so once an oring dries out leaks can be a real problem. Check the pressures with gauges and see what they read. FWIW, my 96 2WD read 245 hi/45 low after a fresh charge of 23 oz. If it is low, vacuum the system down using a vacuum pump and isolate the low side gauge to see if it holds vacuum. If it holds (30 mins or more), charge it with some R-134a with dye. If it returns to 0 you have a leak. With the dye, you'll be able to look at it with a black light and see the leak. Dye won't hurt your system but I'd advise against any leak sealer because those can plug an expansion valve. Dish soap & water in a spray bottle is also good for testing suspect areas but you can't get to everything like the evap or expansion valve. Usually, it's a compression fitting oring or compressor seal (like mine was) on my Nissan that sat for a couple years in a garage. The seal dried out and it was done.
 

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Discussion Starter #10
I have my EPA 608 & 609. Based on what you've tried, I'm guessing another leak. If the compressor is turning (with power directly to it like you did) and the fan is blowing, it should blow cold air if it's still charged. R-134a is a relatively small molecule compared to R-12 so once an oring dries out leaks can be a real problem. Check the pressures with gauges and see what they read. FWIW, my 96 2WD read 245 hi/45 low after a fresh charge of 23 oz. If it is low, vacuum the system down using a vacuum pump and isolate the low side gauge to see if it holds vacuum. If it holds (30 mins or more), charge it with some R-134a with dye. If it returns to 0 you have a leak. With the dye, you'll be able to look at it with a black light and see the leak. Dye won't hurt your system but I'd advise against any leak sealer because those can plug an expansion valve. Dish soap & water in a spray bottle is also good for testing suspect areas but you can't get to everything like the evap or expansion valve. Usually, it's a compression fitting oring or compressor seal (like mine was) on my Nissan that sat for a couple years in a garage. The seal dried out and it was done.
Also very good advice. I'll try and check once this rain calms down and post an update. Thanks!
 

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Discussion Starter #11
So, after a long time (life has been in the way of my truck hobby lol), I got around to checking my pressures with the gauges. With the truck running, AC on high, fans on, etc. my low pressure was sitting at 32 psi and my high was sitting around 25 psi. The compressor was not running, of course. So, I'm wondering, if my high pressure is nowhere near where it should be, am I chasing a leak in the high pressure or a blockage keeping gas from going to the high side?
 

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Mambeau / Admin
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Just for the record, here's the spec's from the 1995.5 / 1996 FSM:

NORMALLY FUNCTIONING REFRIGERATION SYSTEM

Gauge reading:

Low pressure side:
0.15 – 0.25 MPa (1.5 – 2.5 kgf/cm2)

0.15 MPa = 21.76 PSI
0.25 MPa = 36.26 PSI

High pressure side:
1.37 – 1.57 MPa (14 – 16 kgf/cm2)

1.37 MPa = 198.7 PSI
1.57 MPa = 227.7 PSI
 

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Mambeau / Admin
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... I'm wondering, if my high pressure is nowhere near where it should be, am I chasing a leak in the high pressure or a blockage keeping gas from going to the high side?
I don't know enough about A/C to see any difference in these two explanations.

However ...

(I'm not sure how to phrase this ... )

It seems to me there's something else in the overall circuit that's blocking pressure so that you're getting the two different readings on either side of the compressor. In other words - there's still something separating the high and low sides so that they read differently, and I'm not sure it's the compressor.

Is there another valve in the circuit somewhere?

Maybe I'm 'way off base here, but it seems to me the two sides should have settled into the same pressure unless there's something still separating them into two pressure zones.
 

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Discussion Starter #14
I think I am going to try adding some more refrigerant. If that fails, I'll have the system evacuated and check the expansion valve.
 

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Without the compressor running, the system pressure at any point should be the same. The difference you're seeing is likely just a discrepancy in the two gauges. Typically the low pressure gauge is going to be more accurate because it has a much smaller range and the high, a much larger range but we're only talking about a seven psi variance between the two and they're not exactly precision, calibrated instruments. They'll get you close but they're not lab-quality equipment.

Bottom line is you have a leak somewhere. It could be a connection, a hose, compressor, or any other point along the system. If you were to charge the system with any refrigerant, the pressure should increase at every point along the system. If you had a blocked expansion valve, the high pressure would be excessively high and the low pressure excessively low (the compressor would basically be sucking the low side lower and not have any place to push the refrigerant).

Focus on finding the leak first. When your system holds refrigerant without any leaks at all, then you can focus on other issues. At this point, though, you're just wasting effort and refrigerant/money. If it's not jumping out at you, take it to an AC shop and have them look for the leak with a halogen sniffer. You're looking for a small, invisible leak that could be in the engine compartment or in the cab. They can be hard to find, especially if it's a slow enough leak.
 

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With the truck running, AC on high, fans on, etc. my low pressure was sitting at 32 psi and my high was sitting around 25 psi. The compressor was not running, of course.
Despite the switch and fan settings, the compressor won't run until there's enough pressure in the system to safely turn it on. The compressor relies on refrigerant for cooling and the low pressure shut off switch interrupts the compressor electrical circuit if the pressure drops too low.

This is a temperature/pressure chart for R-134a: https://www.forane.com/export/shared/.content/media/downloads/products-documentations/fluorochemicals/forane-134a-pressure-temperature-chart.pdf

Now picture a steel refrigerant cylinder. At a given ambient temperature, a cylinder of refrigerant with one liquid ounce or 20 lbs should have the same pressure. As temperature goes up, so does pressure regardless of the volume of refrigerant. Buy a can of R-134a and connect a gauge to it on a 90F degree day at it will read 104.3 psi. Leave one liquid ounce in it and it will read 104.3 psi.

Based on your low pressure readings, I can tell you there isn't any liquid refrigerant in the system and what gas you do have is only there because the leaking component can hold 30 or so psi and no more.
 

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Discussion Starter #17
Despite the switch and fan settings, the compressor won't run until there's enough pressure in the system to safely turn it on. The compressor relies on refrigerant for cooling and the low pressure shut off switch interrupts the compressor electrical circuit if the pressure drops too low.

This is a temperature/pressure chart for R-134a: https://www.forane.com/export/shared/.content/media/downloads/products-documentations/fluorochemicals/forane-134a-pressure-temperature-chart.pdf

Now picture a steel refrigerant cylinder. At a given ambient temperature, a cylinder of refrigerant with one liquid ounce or 20 lbs should have the same pressure. As temperature goes up, so does pressure regardless of the volume of refrigerant. Buy a can of R-134a and connect a gauge to it on a 90F degree day at it will read 104.3 psi. Leave one liquid ounce in it and it will read 104.3 psi.

Based on your low pressure readings, I can tell you there isn't any liquid refrigerant in the system and what gas you do have is only there because the leaking component can hold 30 or so psi and no more.
This is all very good information, thank you Rick! I'm going to go leak hunting and maybe even replace all the seals in the process.
 
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