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Discussion Starter · #1 ·
We've been having some issues with our air conditioning for some time, and I'm wondering about the pressure switches.

I added some refrigerant at one point, and found that the high side pressure would slowly climb way too high. It would run sometimes over 400 psi, then the system would kick out. It would drop to 3xx psi, then kick back in, then repeat. The fans didn't seem to be turning on, though, and the system seemed to operate better on the highway when there was airflow.

So, my question is: what functions does the high side pressure switch provide? I was under the impression that it would be the switch that would kick out the compressor when it got too high in pressure, but also to turn on the fans. However, I would think that it would cycle out the compressor long before 400+ psi since the fans would be needed at around 214 psi, and that the 400+ psi turn-off might be additional overpressure protection by the ECM.

Can anyone elaborate on this? I'm leaning towards replacing the switch, but I'd like to first better understand the function. I also wouldn't mind understanding the role that the low side pressure switch plays for our traverses specifically (mine being a 2010). Note that I have verified that the fans and relays are functioning properly.

Thanks.
 

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I changed my switch and fixed my car posted pics in the" ac blinks 3times post" most people don't check the high side pressure if your pressure is good on low side and high side is high spiking could have moisture in the system and icing. The switch was easy and self sealing don't have to bleed off the system. Assuming we are talking the same switch. You can check the power into the switch and even check its resistance which I did in the other post if you don't find it I will copy it over for you mine was the very last comments in it. Good luck keep posted what happens cheers.
 

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We've been having some issues with our air conditioning for some time, and I'm wondering about the pressure switches.

I added some refrigerant at one point, and found that the high side pressure would slowly climb way too high. It would run sometimes over 400 psi, then the system would kick out. It would drop to 3xx psi, then kick back in, then repeat. The fans didn't seem to be turning on, though, and the system seemed to operate better on the highway when there was airflow.

So, my question is: what functions does the high side pressure switch provide? I was under the impression that it would be the switch that would kick out the compressor when it got too high in pressure, but also to turn on the fans. However, I would think that it would cycle out the compressor long before 400+ psi since the fans would be needed at around 214 psi, and that the 400+ psi turn-off might be additional overpressure protection by the ECM.

Can anyone elaborate on this? I'm leaning towards replacing the switch, but I'd like to first better understand the function. I also wouldn't mind understanding the role that the low side pressure switch plays for our traverses specifically (mine being a 2010). Note that I have verified that the fans and relays are functioning properly.

Thanks.
If you're talking engine compartment fans....they are cycled by radiator coolant temperature...........many automatically come on if A/C button is turned on to compensate for the additional heat load from the condenser, but neither have anything to do with the high pressure cutout on the A/C line.

High pressure cut out switch's function is only to act a safety device; not to cycle the radiator fans or cycle the HVAC system ....
It cuts power to the compressor to keep the high pressure side hose from rupturing....and when they do, stand clear, they go off like a canon........don't be anywhere under the hood if does. If the refrigerant manifold's high side gauge exceeds 400+ p.s.i. there is definitely a problem........ Assuming low side is within specs....most likely the cause is air entrained in the lines which does not compress as easily as gaseous refrigerant and the sum of the partial pressures exceeds specs. Either the system was so low/discharged that air entered the suction line, or improperly filled where the supply hose was not flushed of air before additional refrigerant was added through the hose.

My .02 - System needs to be evacuated, leak repaired, then refilled with new refrigerant . Then measurement using a two gauge manifold should show both high and low sides within specs. Also if for some reason you plan to change the high pressure cutout switch you had better evacuate the system first before removing because it could fly out with lethal force.
 

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I changed my switch and fixed my car posted pics in the" ac blinks 3times post" most people don't check the high side pressure if your pressure is good on low side and high side is high spiking could have moisture in the system and icing. The switch was easy and self sealing don't have to bleed off the system. Assuming we are talking the same switch. You can check the power into the switch and even check its resistance which I did in the other post if you don't find it I will copy it over for you mine was the very last comments in it. Good luck keep posted what happens cheers.
I stand corrected if the high pressure switch is attached through a Shrader fitting (like a tire) which will prevent leakage if removed....they weren't in the 70s, straight into the high pressure line.
 

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Discussion Starter · #5 ·
Thanks, that does clarify things. My issue is that the radiator fans don't seem to be turning on with the ac, so I'm trying to figure out why. To my understanding, you need airflow over the condenser to remove heat, otherwise you see an increase of high side pressure. We were seeing the pressure buildup when idling on a hot day while the fans weren't running. Once we were driving, things seemed to work much better, so it seems that the fans should be running to keep the airflow over the condenser for things to operate properly. I've read that they should come on when the high side pressure hits around 214 psi, but it doesn't seem to be happening. It does make sense that the fans are strictly controlled by the ECM rather than a pressure switch, though.
 

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Discussion Starter · #6 ·
Maybe a stupid question, but do our Traverse's not have a low side pressure/cycling switch? I haven't been able to find a part number for one online. If it doesn't have one, what method is used for cycling the compressor and to avoid freezeup?
 

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I have a 2010.So I am convinced that there is no low pressure switch unless it is hidden in the back of the car where the low pressure lines run also to rear evaporator.( I have never torn the plastic in back to look) the switch I changed is the High side compressor discharge which is next to the low pressure line into the compressor. The facts I know is that there is voltage input into the switch could be coming from ECU as someone mentioned a wire print would be great.and depending on the pressure it from discharge from the compressor must complete the circuit supplying return voltage to various functions. I know when it is cold out it is tied to the vehicle temp sensors won't turn on compressor. I know other vehicles I have worked on had a very obvious low pressure switch and high pressure switch their names state the obvious function. This vehicle is different from old cars in so many ways that I am still learning myself. I am going to attach a few pics to see if we are on the same page if you find a low pressure switch I would love to see its location I went and looked through my whole system and couldn't find it. Just stating it incase others read this; the BIG line is LOW pressure, the SMALL line is HIGH pressure. This switch in my mind is allot more that just a high overpressure cutout and serves more functions than a classic overpressure switch.
 

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AC light blinking 3 times - no cool air.*FIXED*
Pulled the switch pn 20915 and ohmed it from the 5v input side to all the pins 89to 100kohmsway to high. Good is like 5.4 ohm you do not have to bleed off the pressure of the system to change the switch. As soon as I started the car the a.c. light stayed on may even be possible to slave in new switch. A.c. was low with it engaging clutch was at 20psi serviced to 35 when engaged 48 not engaged. It's Fixed
 

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I have a 2010.So I am convinced that there is no low pressure switch unless it is hidden in the back of the car where the low pressure lines run also to rear evaporator.( I have never torn the plastic in back to look) the switch I changed is the High side compressor discharge which is next to the low pressure line into the compressor. The facts I know is that there is voltage input into the switch could be coming from ECU as someone mentioned a wire print would be great.and depending on the pressure it from discharge from the compressor must complete the circuit supplying return voltage to various functions. I know when it is cold out it is tied to the vehicle temp sensors won't turn on compressor. I know other vehicles I have worked on had a very obvious low pressure switch and high pressure switch their names state the obvious function. This vehicle is different from old cars in so many ways that I am still learning myself. I am going to attach a few pics to see if we are on the same page if you find a low pressure switch I would love to see its location I went and looked through my whole system and couldn't find it. Just stating it incase others read this; the BIG line is LOW pressure, the SMALL line is HIGH pressure. This switch in my mind is allot more that just a high overpressure cutout and serves more functions than a classic overpressure switch.
Seems they kept the same setup in the gen2s but you have to remove the engine or radiator to get access. No low pressure cutout switch or drying tank like the older units.

The system resembles those used in many aftermarket systems which used a temperature sensor located on the expansion valve (or controlled orifice) on the suction line where it enters the evaporator(s). A low refrigerant charge and lower than spec pressure on the suction line will cause external freezing and blockage of the evaporator coils preventing cooling so a temperature sensor will cut power to the compressor clutch and the electric radiator fans if the coolant temperature is within specs.

One would think ice forming on the evaporator coils is a good thing- it is not because at best it will cause frost and only temporarily block the coils to air flow - but the lower mass charge does not have the capacity to extract the mass of heat from the car interior so all you get is a rapid cycling effect that is insufficient to cool the air and extract heat from the mass within the interior. Compressor off, evaporator heats up, valve/coils unfreeze, compressor on, suction pressure rises, lines refreeze, compressor off.......xxxxx

Problem does not appear to be the high pressure cutout - if high pressure is above 400+ and the compressor cuts out and then cuts in again once the high pressure side drops.....it appears to be working in its role as a safety device.

Normal operation is that with the compressor off and allowed to sit for a while both low and high sides should equalize with the same pressure readings. Once in operation the suction (larger pipe) pressure lowers and the exhaust (smaller pipe) pressure rises. A low refrigerant charge will cause the low side to drop below pressure, freeze the coils (open the temps sensor) and cutout the compressor, but this will also cause a lower than spec exhaust (high pressure side).

Seems this is not what OP describes . i.e. a low charge, low pressure side but instead with a higher than spec high pressure side. Regardless of whether a system uses a low pressure cutout switch or a temperature monitoring switch, the high temperature switch should never be cycling the compressor and at 400+ p.s.i. this appears to be the case. So as mentioned previously the problem is likely air in the system which will cause the high side to skyrocket even if the low side is within specs.....with air comes humidity (moisture) and even if the volume of air alone only marginally boosts the high side pressure, the small traces of moisture (absent a dryer or a dryer which has become saturated) can be enough to internally block the small openings in the expansion valve or orifice and stop the flow of refrigerant while the compressor is constantly compressing what little refrigerant there is and pulling a partial vacuum on the suction side until the high pressure becomes so great the cutout kicks in.

My .02 At this point the system needs to be serviced by evacuation until the air is expelled and the moisture removed before refilling - continued addition of refrigerant while the high side is reading 400+ is simply not wise - should the high pressure cutout fail and you exceed test specs something has to give and either the compressor will fail, a line will rupture or a connection/fitting will blow at the under hood condenser or feeding the interior evaporators - and don't be anywhere near one when it does.

BTW - Oil filter is easy to change but there was a tradeoff- so here's where they buried the high pressure switch in the gen2s
 

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Thanks for the info I am always interested to learn extra on a system in case another part of my system fails since I'm not a dealership jockey.
 

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Discussion Starter · #11 · (Edited)
To clarify, the pressure was spiking to 400+ psi after I had recharged it, possibly/probably with a bit too much. It would cool ok on the highway with that charge and would be around 240 psi on the high side, but, when stopped or idling, it would cycle on and off due to the high pressure switch kicking out around 420 psi. I let out some refrigerant to stop it from cycling when stopped (i.e., brought the high side pressure down to 250 psi), but it would no longer cool properly and the pressure would be around 130 psi on the highway, which had me thinking that there may be an airflow problem with the condenser.

It may very well be that there is some air in the system, though. The issues really arose after we took it into the dealer for a timing chain replacement under warranty. The pulled the engine (which is not really necessary apparently) and they pinched a power steering line which shifted and rubbed against the high pressure ac line at the firewall when they put the engine back in. It ended up wearing a hole in the aluminum line. Even with a now noisy power steering pump and leaking ac, they refused to take responsibility for their mistake, but they did do a rough patch job of the line, evacuated the system, and refilled it (still costing me $300 for their mistake). There may be a leak in their repair, though.

PS: is anyone else having issues loading pictures on the forum? I've tried opening the photos that you guys have attached, but I can only get about a third of each image to load before it stops, even after clearing my browser cache.
 

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Discussion Starter · #15 · (Edited)
Has anyone ever replaced the evaporator temperature sensor/switch? Sounds like a big job if it means getting at the evaporator. I don't think that's my issue, but curious of the effort needed nonetheless.
 

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AC light blinking 3 times

AC light blinking 3 times - no cool air.*FIXED*
Pulled the switch pn 20915 and ohmed it from the 5v input side to all the pins 89to 100kohmsway to high. Good is like 5.4 ohm you do not have to bleed off the pressure of the system to change the switch. As soon as I started the car the a.c. light stayed on may even be possible to slave in new switch. A.c. was low with it engaging clutch was at 20psi serviced to 35 when engaged 48 not engaged. It's Fixed
The switch PN 20915, can you get this from O'reilly's/autozone or do you have to go to the dealer?


CB
 

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Hello all,

Not sure if this is still active or if I can get a response. Long story short we got our 2016 traverse from carshop. Was ok, we thought until we got it home. 5 hour round trip, turns out it needed new shocks and struts, new diff, new transmission, new power steering pump nothing paid out of pocket.

Our issue started about 2 weeks ago, car ran great we took it easy due to new tranny. Took my son 15 down the road with the AC going, stopped for about 10 min. Left to go home made a turn and heard a crazy hissing sound. **** off the car, saw green looking coolant on the floor. Not a lot but enough to worry. Check the reserve and it was orange coolant. Waited drove home and it didn't over heat(only 10 min to get home). Started the car and it seemed fine in the driveway. Couple days later we saw it was getting hotter then the normal 210 degrees and I got worried. Noticed the AC light blinks 3 times. Well turns out also the fans never come on now. I have been doing some research and finally saw this thread and I'm trying to understand the lingo when it comes to the AC and the psi upper and lower. I see some comments about switch PN 20915 also thomcat posted a pic of a hose I think caused the hissing. I recently added some more coolant and the fans still don't turn on and blinking AC light. I saw some talk about the engine temp sensor, which is the coolant sensor if I'm right. The temp rises I guess normally but if I'm sitting in traffic I start to over heat. I'm going to test the fan 1 and fan 2 switches. Does anyone know if that hose is bad? Fuses? New temp sensor needed? No OBD2 codes either. Any and all help is very appreciated.i will def be refreshing the page constantly to see any help or advice.
 
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