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AC questions, and is there a workaround?


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So, for those that don't know, my truck is a hodgepodge of wiring, parts, and different model years-which while it runs, it does cause some issues. One of them that I've temporarily found a workaround for, is the AC. Getting it to run through the PCM and actual harness is out of the question-I have no clue how everything was spliced together, and i don't have the time or extra vehicle to use to tear the wiring apart and trace everything down right now. I have been able to get the compressor to activate, by running a relay off the battery, to a toggle switch inside the cab-but, if it's not retarded hot outside, I do have to shut it off periodically, as the lines will freeze up, and it will stop blowing cold air. I'm guessing this is because I don't have the low pressure switch and the high pressure switch in the system, but is there a way to get those to activate, while running power directly off of the battery? I'm not entirely sure how those two exactly work, to see if its even possible to do. Any ideas?

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just run the high and low pressure switches in series with your clutch engagement circuit...which probably means the clutch gets the 12 volts straight off the relay, then it's ground will then be hot side running back through the 2 switches... Then finally back to ground.That way, if you have either low switch cut out (low pressure from not enough refrig.) or high switch cut out (too much head pressure from over charging or iced up evaporator) it will "open" the circuit and prevent the compressor from engaging.

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ok, I had to run out and check my cows in this storm... and replayed your question in my head.Run the circuit so both pressure switches are part of the energizing loop in the relay. The main power out (from relay) should only go to the compressor only. This will isolate the higher amp loads to just between the relay and compressor.This way, only minimal amps will be going through the switches, not the whole load created with the compressor.Those switches, (which would be wired in series.. would only then complete the relay activation circuit) would not matter which switch is wired first. Both would be normally 'closed'... and if too high or too low a pressure is encountered, the respective switch would 'open' and then would shut down the relay.. which would de energize the compressor.Are you certain you may have just a tad too much refrigerant in your system? I've put a little too much in a tractor or 2 with similar icing up conditions.

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Yeah that sounds about right. Normally the hi/lo switches are run with the PCM so when there is full throttle operation or other system malfunction the PCM can block out the A/C system as well. But your method will work just as well too. As long as the main amperage draw is not routed through the hi / lo switches your good. :wink:

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OK, so just to make sure I'm reading this right, I run the high/low pressure in series with the energizing circuit for the AC-ie pin 86 on the relay, so that it acts as an automatic cutoff for the AC if the pressure/temps get too high/low, and leave everything else alone...As far as there being too much refrigerant, I was pretty careful when I filled it last summer, and the only time I have issues is when it's just warm enough to want AC, but not super hot...the warmer it is outside, the less times I have to shut if off manually to unfreeze the lines...

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A/C lines shouldn't freeze. This is a sign of low freon pressures on the low side. The lower the low side pressure get the colder it gets. So a typical automotive A/C unit is charged to roughly 35-40 PSI (R134a) and a normal house refrigerator is charged to 2-5 PSI (R12 days when I use to work with it). So I would verify the freon pressures again and be sure there is enough freon in the system.Dis-regard the red line I goofed...post-2-138698200102_thumb.jpg

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OK, so just to make sure I'm reading this right, I run the high/low pressure in series with the energizing circuit for the AC-ie pin 86 on the relay, so that it acts as an automatic cutoff for the AC if the pressure/temps get too high/low, and leave everything else alone...

As far as there being too much refrigerant, I was pretty careful when I filled it last summer, and the only time I have issues is when it's just warm enough to want AC, but not super hot...the warmer it is outside, the less times I have to shut if off manually to unfreeze the lines...

ok, follow my trail here... the dashed lines (-----) means 'wire'.

BATTERY (12 POS)--------------(FUSE, 10 AMP)----------(SWITCH IN CAB)------(PRESSURE SWITCH #1)-------

------(PRESSURE SWITCH #2)-------------(RELAY ACTIVATION COIL)----(wire to ground IF relay is not self grounding)

then, another fused source of 12 pos: BATTERY(12 POS)-----------(FUSE 15A?)---------(RELAY, LINE IN)

(RELAY, LINE OUT)-------------(COMPRESSOR)---------(IF NEEDED, GROUND.) SOME COMPRESSORS ARE SELF GROUNDING (one wire units). If you have 2 wire, one wire will take the 12 volts from relay, the other is grounded.

Typical relays with have 3 or 4 terminals. 1 for relay activation, 1 for 12 volts in (line), 1 for 12 volts out to 'load', and possibly relay ground. Most are self grounding

- - - Updated - - -

OK, so just to make sure I'm reading this right, I run the high/low pressure in series with the energizing circuit for the AC-ie pin 86 on the relay, so that it acts as an automatic cutoff for the AC if the pressure/temps get too high/low, and leave everything else alone...

As far as there being too much refrigerant, I was pretty careful when I filled it last summer, and the only time I have issues is when it's just warm enough to want AC, but not super hot...the warmer it is outside, the less times I have to shut if off manually to unfreeze the lines...

ok, follow my trail here... the dashed lines (-----) means 'wire'.

BATTERY (12 POS)--------------(FUSE, 10 AMP)----------(SWITCH IN CAB)------(PRESSURE SWITCH #1)-------

------(PRESSURE SWITCH #2)-------------(RELAY ACTIVATION COIL)----(wire to ground IF relay is not self grounding)

then, another fused source of 12 pos: BATTERY(12 POS)-----------(FUSE 15A?)---------(RELAY, LINE IN)

(RELAY, LINE OUT)-------------(COMPRESSOR)---------(IF NEEDED, GROUND.) SOME COMPRESSORS ARE SELF GROUNDING (one wire units). If you have 2 wire, one wire will take the 12 volts from relay, the other is grounded.

Typical relays with have 3 or 4 terminals. 1 for relay activation, 1 for 12 volts in (line), 1 for 12 volts out to 'load', and possibly relay ground. Most are self grounding

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Got it. That's what I was thinking, just wanted to make sure. I'll try and get to that over the next couple of days, if time permits...Been working like a dog lately, and when I get home, typically eat dinner and go to sleep anymore!

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