A/C not blowing cold air

Tiny
BOBK123
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I don't think I can discharge and recover the refrigerant in the system without special equipment. So I asked a local mechanic about doing the service. I can get the part and bring it in. But he said I can try jumping the pressure switch to see if the switch is bad. Does this make sense?
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Friday, July 9th, 2021 AT 5:44 PM
Tiny
KASEKENNY
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I thought about that earlier but this is a dual pressure switch which means it shuts down when pressure is high or low. They are normally 3 wire sensors which means it sends a signal to the control module. However, looking at this again that is not the case on this vehicle.

Your pressure switch is an on off switch so you can jump it. Basically it looks for 12 volts or 0 volts. So just disconnect it and put a wire between the two terminals and then turn the ignition and A/C on. It should come on. This confirms the sensor is the issue.

Great idea and glad you mentioned it to make me look again. That's what I get for assuming.
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Saturday, July 10th, 2021 AT 4:47 PM
Tiny
BOBK123
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Hi Kenny,

I removed the pressure sensor connector and jumped it, but the compressor clutch did not start spinning, so no luck. But I see there are 4 terminals on this connector, in a diamond type pattern. Blue/red and yellow/black are opposite from each other, these are the terminals I jumped. The other two look like blue/black and green.

Just to confirm I did the right thing, I jumped the points on the connector, not on the switch itself.

Then I checked for voltage on the connector. Blue/red has 14v (I probed blue/red and battery -). Yellow/black I assume is ground. But when I probe yellow/black and battery + I get no voltage reading.
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Sunday, July 11th, 2021 AT 8:54 AM
Tiny
KASEKENNY
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That is correct. Basically they are using this switch to control the fan speed as well to keep the engine cool and air flow over the condenser.

This is progress. This is showing that the module is not grounding this circuit.

Here is what you should have: At the control module, it needs to see 12 volts on pin 1. This shows that the pressure is correct and it is ok to turn the compressor on.

Then the control module will ground the relay on pin 9 and you will see 0-1.5 volts at the control module on this wire. You have battery voltage which shows it is not grounding the circuit.

You have 0 volts on pin 1 so it is cutting the compressor off which is why the two wires going to the PCM are not reading the correct voltage either because this is the AC module telling the PCM that the compressor is off.

If jumping that switch does not cause the compressor to come on then we are back to the control module.

What I would do from here is just make sure you don't have a wiring issue from the switch to the module by jumping the switch again and then check voltage at the module on this wire, Pin 1. You should have the same voltage that you do at the switch. If you do then the module is the issue.

Another way to confirm this is to just leave everything connected and jump 12 volts from the battery directly to Pin 1 of the module. If the compressor comes on then it is not getting 12 volts and you have a wiring issue.

Take a look at this below. Please let me know if you have other questions and what you find. Thanks
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Sunday, July 11th, 2021 AT 9:27 AM
Tiny
BOBK123
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Thanks for all the help Kenny! I had to think this through after reading it a few times. But now I do understand what you're saying. We're trying to find out if there's a wiring issue between the pressure switch pin 4 (yellow/black) and the control module pin 1 (not sure why it says yellow/blue in the voltage table diagram? But I assume this is the same wire). I may not get to testing this till the weekend. But I will let you know as soon as I find out.
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Monday, July 12th, 2021 AT 5:44 AM
Tiny
KASEKENNY
  • EXPERT
Don't worry about the wire color. That could be an issue with the wiring diagram. They often changed the color wire when the run out of one, they switch to another.

Let us know what you find when you get to it. Thanks
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Monday, July 12th, 2021 AT 5:59 PM
Tiny
BOBK123
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Hi Kenny,

I completed both the tests you suggested, and I think it's looking like it's a bad control module. Please confirm. This is what I just did:

I jumped the pressure switch, then with the engine running and the AC/blower on, I checked voltage at pin 1 of the control module. I read 14v, same voltage present at pin 1 of the switch (I did this by probing with my meter on the control module, red to pin 1 and black to pin 4 ground). So I assume this confirms the wiring between the pressure switch to pin 1 of the control module is good.

Then I reconnected the pressure switch connector, and jumped 12v directly from battery + to control module pin 1. With the engine running and AC/blower on, the compressor clutch did not come on - still no A/C.

One Question - do we know for sure that the pressure switch is good? (If the pressure switch was the problem, would the A/C have turned on when I jumped it?)

Thank you!
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Sunday, July 18th, 2021 AT 12:33 PM
Tiny
KASEKENNY
  • EXPERT
That is excellent. You are exactly correct. If you look at the chart and wiring diagram below.

You need 12 volts at pin one in order for the module to know that the pressure is ok. If you jumped the switch and then checked voltage at the module using the modules ground and you have 12 volts on your meter then you verified the entire circuit.

If the module has 12 volts on pin 1 and it still does not come on then the module would be the issue.

However, you appear to have an issue with the switch as well.

The jumping of the switch is a clear and simple test. If you have to jump the switch in order to get 12 volts to the module then the switch has failed.

If it were me, I would replace the module and then jump the switch again which should cause the compressor to come on. If it does, replace the switch. However, if you want to put the switch on it now, I would understand because this is a simple on off switch based on pressure. So either it is closed or open based on the pressure and if the pressure is correct and it still is open then it is faulty.
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Monday, July 19th, 2021 AT 9:00 AM
Tiny
BOBK123
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Thank you! Since the pressure switch needs to be replaced I will first have that done by my mechanic. I went ahead and ordered the part. I'll let you know when that's done.

Is there a chance that the pressure switch is the only problem? I know we jumped the switch to determine it is bad. If the bad pressure switch is staying open will this prevent the compressor from turning on, even when it is jumped?
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Monday, July 19th, 2021 AT 12:39 PM
Tiny
KASEKENNY
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Normally yes. However, when you jump it the compressor should come on if it were the only issue. All the switch does is provide 12 volts to the module which tells it the pressure is not to low or high. So if you not only jumped it but then applied 12 volts to it and it still did not come on then we have another issue.

Let us know how you make out with this. Thanks
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Monday, July 19th, 2021 AT 7:10 PM

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