A/C recharge blows very cold at first, but then...

[ulycyc]

If the IAT is bad it usually will set a trouble code. Showing 32deg will command a fuel trim for colder weather. It may make the car run a little rich or misfire but not really effect the AC.

 

[richardnewton]

Is your scanner showing the IAT in degrees Centigrade or Fahrenheit?

If the former (which I suspect), there is some heat from the sun and engine, so 32c might not be far off the mark.

 

[FSUDAL]

Is your scanner showing the IAT in degrees Centigrade or Fahrenheit?

If the former (which I suspect), there is some heat from the sun and engine, so 32c might not be far off the mark.

All temps for IAT (which is referred to as MAP sensor in part nomenclature) are Fahrenheit. Maybe the temp part of sensor is not used for this car and just the pressure? I replaced the sensor and it still shows 32 degrees Fahrenheit even though outside temp is 73.

I did notice that ac high side pressure is about 150 psi and quickly rises to 189 at 1200 rpms before compressor cycles off until pressure drops back to 150. The scanner readings seem higher than what the AC manifold gauge showed ,(granted the other day). At the time high side pressure was about 125 and only climbed to 131 when rpms increased to 1200. Maybe ac pressure sensor is incorrect?

 

[richardnewton]

Isn't the MAP sensor "Manifold Absolute Pressure sensor"? If so, 32kpa might not be an unreasonable idle reading.

It is possible that your scanner has mislabeled this item and its units?

 

[ulycyc]

IAT and MAP are different sensors and report different information. The MAP will only show pressure and the IAT will only show incoming outside air temps. Take a picture of the scanner screen and post it.

 

[FSUDAL]

IAT and MAP are different sensors and report different information. The MAP will only show pressure and the IAT will only show incoming outside air temps. Take a picture of the scanner screen and post it.

Please see attached pic. Would you know how I can locate intake air temp sensor #2? My search lead me to believe it is combined with MAP sensor. Please let me know if you need anything else. Thank you.

 

[ulycyc]

You are correct GM made a "multi-purpose" switch for your car. You learn something new everyday The map sensor also reports air temp. You also have a IAT sensor mounted somewhere in the air intake box around the air cleaner area. Which one is 1 &2 I don't know. Disconnect the plug from the one by the air filter and see what happens on your scanner.

 

[richardnewton]

On our 2.4L Lacrosse, one sensor on the air duct is responsible for both MAF & IAT readings.

 

[FSUDAL]

On our 2.4L Lacrosse, one sensor on the air duct is responsible for both MAF & IAT readings.

I unplugged MAF sensor and intake air temp #1 went from 99 degrees Fahrenheit to -40. Cooling fans also increased speed from 1 to 2 on scanner. MAF went from 0.67 lb/mn to 0.

Unplugged MAP sensor (barometric pressure) and there was no change in intake air temperature #2. Still stuck on 32 degrees Fahrenheit. MAP went from 14psi to 0. No change in fan speed.

Today the increased fan speed (while MAF sensor is unplugged) did not help cool AC at all. I thought increased fan speed was part of solution since fan speed doesn't increase when AC is turned on (cooling fans stay at low speed). This is why I am interested in finding out why IAT sensor #2 stays at 32 degrees Fahrenheit. Thinking 33 degrees keeps fans from increasing speed?

Scanner ambient temp shows 68 and temp on clock shows 74. Cabin temp is 85 (sunny out). AC high side pressure goes up to 193 psi and stays around there at 2000 rpms. When idling high side pressure goes down and stays around 150psi. I expected pressure to build then drop as the compressor cycles? Maybe I didn't wait long enough for compressor to kick off...

Is there actually an IAT #2 on this car?

What would you do next to find ac problem?

Thank you.

 

[ulycyc]

As I said earlier the other iat sensor is mounted in or around the air filter box or hose going into the throttle body.

 

[FSUDAL]

As I said earlier the other iat sensor is mounted in or around the air filter box or hose going into the throttle body.

Thanks for the quick reply. My research shows that MAP sensor also includes a temperature sensor (just like MAF).

I think IAT #1 is combined with MAF (by throttle body) and IAT #2 is combined with MAP (on top of filter box).

Please let me know if you see IAT#2 somewhere else or if there is even an IAT #2 that the car uses. I am assuming it does since scanner shows reading and not NA.

 

[FSUDAL]

I spent some time today to get readings from the AC system (see below). Why do you think the system is not cooling properly?

Ambient Temperature 97 degrees Fahrenheit
AC static pressure 110 psi

While idling at 750 rpms for 15 minutes:

• Cooling fans are running at low speed
• Low side pressure is 50 psi
• High side pressure slowly increases/decreases between 165-180 psi
• Inside vent temperature is 60 degrees Fahrenheit

While maintaining constant 1550 rpms for 15 minutes:

• Cooling fans are running at low speed
• Low side pressure is 65 psi
• High side pressure slowly increases/decreases between 155-165 psi
• Inside vent temperature is 70 degrees Fahrenheit

After 10 minutes of idling at 750 rpms again:

• Cooling fans are running at low speed
• Low side pressure is 56 psi
• High side pressure slowly increases/decreases between 150-160 psi
• Inside vent temperature is 64 degrees Fahrenheit

10 minutes after car has been shut off:

• Low side pressure is 108 psi
• High side pressure is 110 psi

Thank you.

 

[ulycyc]

This will answer most of questions about a/c gauge readings. Also remember humidity and the quality of your gauge set will vary your results. Not sure what you are using but a gauge set from Harbor freight or Walmart is not what a professional shop would be using.

Understanding Normal AC Pressure Gauge Readings

Learn why normal AC pressure gauge readings are essential for diagnosing car AC problems. Don't rely on just the low-pressure gauge

ricksfreeautorepairadvice.com

 

[FSUDAL]

This will answer most of questions about a/c gauge readings. Also remember humidity and the quality of your gauge set will vary your results. Not sure what you are using but a gauge set from Harbor freight or Walmart is not what a professional shop would be using.

Understanding Normal AC Pressure Gauge Readings

Learn why normal AC pressure gauge readings are essential for diagnosing car AC problems. Don't rely on just the low-pressure gauge

ricksfreeautorepairadvice.com

Thanks for providing the link. Ironically, I had printed off that material and have been using it. It was very helpful.

The AC manifold gauges matched the scan tool pressure reading (at least the high side pressure since there is no low side pressure on my scan tool), so I am assuming the gauges are accurate. I forgot to put that the humidity was 44%. It seems that my high side pressure may be a little low. If the correct amount of refrigerant is in the system and there are no leaks (based on what shop said last time I was there) does that mean that I have a bad compressor or could something else be causing the problem?

 

[ulycyc]

Your numbers are not too far off but there could be a problem. It's possible it's low or overfilled or the freon is contaminated. Your year not sure check the sticker if it takes freon 134a or 1234yf. They do mix if the shop did it but if mixed it can break down the oil faster. I would check all that before replacing hard parts like the compressor.

 

[richardnewton]

Check the cabin air filter. If that is dirty, the restricted airflow might solve some of your issues (but I don't think all).

Nissens does not recommend testing above 95F ambient (we used a few of their compressors and they grenaded quickly so only use OEM but their poster might be useful lol).

https://nissens.com/Admin/Public/Download.aspx?file=Files%2FFiles%2FAuto%2FPosters%2FNissens_AC_System_Diagnostics_Poster_98x68+-+Operating+Pressures+R134A+-+ENG.pdf

 

[FSUDAL]

Check the cabin air filter. If that is dirty, the restricted airflow might solve some of your issues (but I don't think all).

Nissens does not recommend testing above 95F ambient (we used a few of their compressors and they grenaded quickly so only use OEM but their poster might be useful lol).

https://nissens.com/Admin/Public/Download.aspx?file=Files%2FFiles%2FAuto%2FPosters%2FNissens_AC_System_Diagnostics_Poster_98x68+-+Operating+Pressures+R134A+-+ENG.pdf

Thanks for the suggestion. Cabin filter is new, and airflow is working well.

I am haven't worked much on AC before. Always was afraid and avoided it at all costs due to the many dangers. Never heard of compressors exploding. My scanner indicated that the ambient temperature was 97 degrees Fahrenheit, but it was not actually that hot outside. I guess the sensor factors in some of the heat from the engine.

 

[FSUDAL]

Your numbers are not too far off but there could be a problem. It's possible it's low or overfilled or the freon is contaminated. Your year not sure check the sticker if it takes freon 134a or 1234yf. They do mix if the shop did it but if mixed it can break down the oil faster. I would check all that before replacing hard parts like the compressor.

I took it to Firestone. I would hope they knew to put 134a in it but maybe their machine wasn't clean. I don't think they would put 1234yf since I overheard the guy at the counter telling someone on the phone how ridiculously expensive it is but who knows.

I am guessing that there is no way for me to check to see how much is in the system (other than using the manifold gauges), what type of freon they put in, or if it is contaminated. Let me know if I am wrong.

Would you have a national chain that you would recommend? I am in Ohio. If major parts need to be replaced, I will want them to evacuate the system so that I could change them myself.

 

[richardnewton]

Cabin filter is new, and airflow is working well.

Good

Never heard of compressors exploding.

I meant that they were noisy and failed after a couple of years. No explosions!

 

[HotZ28]

There is also a control valve in the compressor which can fail that varies compressor operation. It can be a manual valve, or electrical valve. If it it is failing, it would be best to replace the compressor, rather than trying to replace individual parts! Be sure to get get the whole kit that includes the compressor, expansion valve & the accumulator/drier. Some kits even offer a new condenser as part of that.