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What causes High Pressure in AC System #5125064
06/04/19 12:32 PM
06/04/19 12:32 PM
Joined: Apr 2018
Posts: 148
Azerbaijan
NICAT Offline OP
NICAT  Offline OP

Joined: Apr 2018
Posts: 148
Azerbaijan
Hi.
AC compressor was leaking. Took it to repair shop.
When i went to get it i was suprised that they have removed 2 sensors on it and closed the holes.
They claimed that those sensors were too bad, are common point of the leak, and are unnecessary. To proof it, they told that new compressors for the same model cars do not have those sensors.

I made some research. There are total 3 sensor on the AC system.
One sensor on hose (low pressure sensor). If there is no freon, it breaks the circuit.
And 2 Sensors on the compressor. One is High pressure sensor (ON/OF sensor. it increases fan speed if there is high pressure) and the other is Ultra High Pressure sensor. Which breaks the circuit again in orter the save AC (or may be prevent freon leak through the valve)

Actually without those sensors AC can actually run. But without any protection. We can make Fan run at its maximum speed all the time at the cost of fan life.

I am planning to buy replacement Compressor. it is 70$. They will install it for free. But since it is summer, it is difficult to find one.
So i want to use this for a while.
The question is, Is there anything that i can do in order to reduce chance of high pressure ? What causes High Pressure in AC System ? Higher RPMs ? or when AC runs for a long period of time or Stop-&-Go Traffic ?

Regards.



Last edited by NICAT; 06/04/19 12:33 PM.
Re: What causes High Pressure in AC System [Re: NICAT] #5125078
06/04/19 12:46 PM
06/04/19 12:46 PM
Joined: Dec 2006
Posts: 8,744
Canuck living in California
KrisZ Offline
KrisZ  Offline

Joined: Dec 2006
Posts: 8,744
Canuck living in California
As you noted these sensors are mainly there to protect the system. There are variatey if scenerios where the system can run high pressure, like the evaporator coil freezing up in high humidity, low wet bulb temp situations.
If your condenser doesn't get proper airflow, due to fan failure or something physically blocking it, the system will run higher pressures.
If the system is overcharged, it will run higher pressures.

I'm sure there are other scenarios as well.

Last edited by KrisZ; 06/04/19 12:46 PM.

2015 Grand Caravan 3.6L - 31k miles.
2006 Mazda 3 2.0L - 171k miles
Re: What causes High Pressure in AC System [Re: NICAT] #5125079
06/04/19 12:46 PM
06/04/19 12:46 PM
Joined: Oct 2004
Posts: 9,135
Cincinnati, OH, USA
bullwinkle Offline
bullwinkle  Offline

Joined: Oct 2004
Posts: 9,135
Cincinnati, OH, USA
High engine RPMs, combined with high ambient temperatures, usually in stop & go driving. Often combined with a bad fan clutch, overcharged system, or bad electric fan/switch, & a dirty condenser. How hot does it get in Azerbaijan? 35C or so?


06 Ram 3500 CTD 4X4(FG Venturi), 93 GMC C3500 6.2, 89 F-450 7.3, 98 XJ 4.0(XG8A), 05 xB(XG3600), 18 Transit 3.7, 03 Merc Grand Marquis 4.6 2V(XG2)
Re: What causes High Pressure in AC System [Re: bullwinkle] #5125082
06/04/19 12:48 PM
06/04/19 12:48 PM
Joined: Apr 2018
Posts: 148
Azerbaijan
NICAT Offline OP
NICAT  Offline OP

Joined: Apr 2018
Posts: 148
Azerbaijan
Hi. Thanks for detailed explanations smile
It is 45C Max. Average in summer is 41/42 (afternoon)


Last edited by NICAT; 06/04/19 12:51 PM.
Re: What causes High Pressure in AC System [Re: NICAT] #5125103
06/04/19 01:11 PM
06/04/19 01:11 PM
Joined: Sep 2014
Posts: 1,676
Toronto Canada
WobblyElvis Offline
WobblyElvis  Offline

Joined: Sep 2014
Posts: 1,676
Toronto Canada
You want to make sure the condenser coil is clean and free of bugs/debris. This will help keep the pressure down and run more efficiently.

Re: What causes High Pressure in AC System [Re: NICAT] #5125104
06/04/19 01:11 PM
06/04/19 01:11 PM
Joined: May 2012
Posts: 6,709
Fort Lauderdale, FL
DoubleWasp Offline
DoubleWasp  Offline

Joined: May 2012
Posts: 6,709
Fort Lauderdale, FL
Consider that they are performing a modification that may reduce the life of the fan, and that when it fails there will be absolutely nothing to stop the system from going ridiculously overpressure.

the real question is, why don't they have it on the newer models? Is it perhaps because they use a compressor with a pop off valve that protects the system, and a fan management system that negates the need for a fan pressure switch? perhaps the newer model has a fan management system that automatically kicks the fan up high simply from electronically sensing compressor activation?

this is the way that it is done on most vehicles, so it is important enough to know why these changes were made and how the system works on the newer models.

If they were really smart, what they would do is eliminate the 2 sensors that you mentioned, and then replace your low pressure switch with a trinary switch to manage all three functions from a single point. That would leave you without all of the extra connections and still maintain all of the functions that you described above.


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Re: What causes High Pressure in AC System [Re: NICAT] #5125106
06/04/19 01:16 PM
06/04/19 01:16 PM
Joined: Jun 2003
Posts: 19,176
Apple Valley, California
Chris142 Offline
Chris142  Offline

Joined: Jun 2003
Posts: 19,176
Apple Valley, California
Not enough air flow over the condenser and over charging will both create high pressures. No air flow can cause the pressures to go ballistic I just a few seconds.

Your ac shop are absolute idiots! Pull your car from them and get it fixed properly. Do these dummies even have an ac machine or are they still charging with small cans?


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87 F250 Valvoline 15w40
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Re: What causes High Pressure in AC System [Re: NICAT] #5125107
06/04/19 01:16 PM
06/04/19 01:16 PM
Joined: Sep 2015
Posts: 1,936
USA
mk378 Offline
mk378  Offline

Joined: Sep 2015
Posts: 1,936
USA
When it does go ridiculously overpressure, either the relief valve will open if it has one, or some part (usually the high side hose) will burst. Either case will cause loss of most or all of the refrigerant. The relief valve doesn't always close properly. If someone is working under the hood at the time, a bursting hose is a personal injury risk.

Cross that shop off of your list of places to use.

Re: What causes High Pressure in AC System [Re: DoubleWasp] #5125115
06/04/19 01:29 PM
06/04/19 01:29 PM
Joined: Apr 2018
Posts: 148
Azerbaijan
NICAT Offline OP
NICAT  Offline OP

Joined: Apr 2018
Posts: 148
Azerbaijan
Originally Posted by DoubleWasp

the real question is, why don't they have it on the newer models? Is it perhaps because they use a compressor with a pop off valve that protects the system, and a fan management system that negates the need for a fan pressure switch? perhaps the newer model has a fan management system that automatically kicks the fan up high simply from electronically sensing compressor activation?



It is because, on the hose, in my model there is 2 pin sensor. Low pressure sensor. ON/OF. it breaks the circuit if there is no freon.
But in newer models there is 3 pin sensor on the same hose. which gives clear information to the ECU about the pressure in the system. So ECU knows if the pressure is Low, High and Too High.
So one sensor+ ECU does the job of 3 old sensors smile
This sensorless compressors misleaded the shop.

Last edited by NICAT; 06/04/19 01:30 PM.
Re: What causes High Pressure in AC System [Re: NICAT] #5125121
06/04/19 01:40 PM
06/04/19 01:40 PM
Joined: Sep 2015
Posts: 1,936
USA
mk378 Offline
mk378  Offline

Joined: Sep 2015
Posts: 1,936
USA
If you're saying the original compressor didn't have sensors because the car has a 3 wire sensor somewhere else and it's integrated with the ECU, then buying the wrong compressor and just leaving the extra sensors unconnected would be OK.

It doesn't seem that you're saying that though.

Last edited by mk378; 06/04/19 01:41 PM.
Re: What causes High Pressure in AC System [Re: WobblyElvis] #5125124
06/04/19 01:42 PM
06/04/19 01:42 PM
Joined: Sep 2008
Posts: 209
Greece
berlyn Offline
berlyn  Offline

Joined: Sep 2008
Posts: 209
Greece
+1

Re: What causes High Pressure in AC System [Re: mk378] #5125127
06/04/19 01:42 PM
06/04/19 01:42 PM
Joined: Apr 2018
Posts: 148
Azerbaijan
NICAT Offline OP
NICAT  Offline OP

Joined: Apr 2018
Posts: 148
Azerbaijan
Originally Posted by WobblyElvis
You want to make sure the condenser coil is clean and free of bugs/debris. This will help keep the pressure down and run more efficiently.


Yes it is clean. i cleand it myself by removing all the bugs one by one smile
Originally Posted by Chris142
Not enough air flow over the condenser and over charging will both create high pressures. No air flow can cause the pressures to go ballistic I just a few seconds.

Your ac shop are absolute idiots! Pull your car from them and get it fixed properly. Do these dummies even have an ac machine or are they still charging with small cans?


They were just compressor rebuilders.
Not charging.
Surprsingly even the most famous charging shop in the country, told me "Dont worry. they have done the right thing" smile



Originally Posted by mk378
When it does go ridiculously overpressure, either the relief valve will open if it has one, or some part (usually the high side hose) will burst. Either case will cause loss of most or all of the refrigerant. The relief valve doesn't always close properly. If someone is working under the hood at the time, a bursting hose is a personal injury risk.

Cross that shop off of your list of places to use.


It has relief valve. But as you stated, it may not function properly all the time.

Re: What causes High Pressure in AC System [Re: NICAT] #5125187
06/04/19 02:33 PM
06/04/19 02:33 PM
Joined: Dec 2016
Posts: 9,119
Waco, TX
Linctex Offline
Linctex  Offline

Joined: Dec 2016
Posts: 9,119
Waco, TX
I do not envy you.... it must be difficult finding a good mechanic in Azerbaijan


"The evidence demands a verdict".
(Re:VOA)"it's nearly impossible to actually know the particular additives that are in there at what concentrations."
Re: What causes High Pressure in AC System [Re: Linctex] #5125192
06/04/19 02:46 PM
06/04/19 02:46 PM
Joined: May 2019
Posts: 241
USA
AC1DD Offline
AC1DD  Offline

Joined: May 2019
Posts: 241
USA
@NICAT

Best bet for good service would be in Tbilisi, Georgia. Have you thought of that? It's not that far from you.

Re: What causes High Pressure in AC System [Re: Linctex] #5125195
06/04/19 02:55 PM
06/04/19 02:55 PM
Joined: Apr 2018
Posts: 148
Azerbaijan
NICAT Offline OP
NICAT  Offline OP

Joined: Apr 2018
Posts: 148
Azerbaijan
Originally Posted by Linctex
I do not envy you.... it must be difficult finding a good mechanic in Azerbaijan


In my bmw, there was fluctuating rpm problem.
Too much work done on the engine, transmission, tons of money was spend. In the end it turned out to be wrong oil level in the gearbox. They didn't know about ZF's oil change guide. They believed that they should fill as much oil as they could.

Actually the main reason is that, if a kid is very bad at school, (not always, but most of the time because of low IQ) His parents find some mechanics. So their son can learn and have some practice near him. And become a mechanic in the future.
So due to Natural Selection :), Most of the mechanics in the country are the ones who were very bad at school.

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