A/C Question

[blown240]

My AC works great when its cold out, but doesnt blow cold when its warm out. I changed both pressure switches, and had the shop put the correct amount of freon in it. There is an Evap code, which ive read can cause AC issues since apparently its on the same fuse as the AC switches.

I think my problem may be with the compressor clutch though. I have noticed that it will stop cooling sometimes on acceleration, and cool on deceleration. Almost like engine load affects it. Seems like I may need a new compressor clutch.

Thoughts? 04 Yukon XL, 190k miles.

 

[Fless]

I seriously doubt that the evap code (which one?) is causing any issue with the HVAC system.

 

[nonickatall]

The EVAP code definitely has nothing to do with your air conditioning.

The magnetic clutch switching on and off is normal; it generates pressure in the air conditioning system, and when the expansion valve has enough pressure, the compressor switches off.

That's not unusual at all.

If your air conditioning is warm at high temperatures, get out of the car and feel the air conditioning lines under the hood on the passenger side. You should feel a noticeable temperature difference between the low-pressure and high-pressure sides. This will show you whether your air conditioning is cooling at all. Of course, it's possible that you have a problem with an actuator, for example. I had that once with my truck; especially on longer drives, only hot air would suddenly come out. It worked perfectly fine on shorter trips. It turned out that an actuator on the lower passenger side was defective. Since I replaced it, the problem has never occurred again.

I don't think your problem is with the magnetic clutch, because it either engages or it doesn't. While it's theoretically possible that such a magnetic clutch could have a loose connection and sometimes work and sometimes not, I've never encountered such a case.

But as I said, feel your air conditioning lines and see if you have a significant temperature difference. If so, and it still doesn't get cold, you have a problem with your climate control system or actuators.

If it doesn't get warm, the system could be incorrectly charged, the magnetic clutch could be defective, the magnetic clutch relay could be defective, or it could also be a control unit issue.

 

[TJ Baker]

There is an Evap code, which ive read can cause AC issues since apparently its on the same fuse as the AC switches

There are no fuses on the A/C switches, they are 0-5 volt sensors directly connected to the PCM or HVAC modules.

have noticed that it will stop cooling sometimes on acceleration, and cool on deceleration. Almost like engine load affects it.

FWIW, anyone who has an OBDII adapter and an app like Car Scanner, Torque Pro, OBD Fusion etc. can monitor the AC System high pressure sensor. This quite clearly shows compressor engagement/disengagement as the pressure rapidly rises or falls. The PID is $1144 and is read from the PCM with the usual service/mode $22 request. It is more difficult to read other HVAC related live data as the HVAC control modules do not support service/mode $22.

 

[blown240]

Thanks for the replies!

I’ll check the temp if the lines as mentioned.

I don’t have a obd scanner that will read the AC, but I can use my laptop to read the CAN.

 

[TJ Baker]

Thanks for the replies!

I’ll check the temp if the lines as mentioned.

I don’t have a obd scanner that will read the AC, but I can use my laptop to read the CAN.

Not CAN as it is commonly used today. Maybe most see "CAN" as a generic term but when I see "CAN" I think of ISO 15765-4, a 2 wire system with high and low signal lines. You don't have that in your 2004 Yukon. You have SAE J1850VPW, the older single wire class 2 data.

At any rate, reading and monitoring the high pressure sensor is most informative while driving down the road, not so useful when parked. The system behaviour is vastly different when travelling with a constant forced airflow through the condenser coil due to the speed of the vehicle. Plus, apps like Car Scanner can record the data for review later so you can voncentrate on driving instead of looking at a phone or laptop. How does your laptop interface with the OBDII?? WiFi or Bluetooth adapter maybe?

 

[Marky Dissod]

My AC works great when its cold out, but doesnt blow cold when its warm out.

Can you drive without stopping the vehicle IN WARM / HOT weather for 5-10min?
If so, does the AC still underperform? Specifically, WHEN does it underperform?

Several of us have had issues with AC underperformance @ idle when the vehicle is stopped or going dreadfully slowly in stop'n'go traffic.
If your AC is ok in very hot weather, UNLESS you're crawling in traffic or stopped, solution for that is:
a) GM TSB (sorry, forgot number?) admits the mech clutch fan can't generate enough airflow through the AC condenser @ idle in some very hot conditions.
GM installs a lil electrical helper fan in FRONT of the condenser.
b) replace your mech clutch fan with a pair of '05 (or newer!) electrical fans, requires a bit of installation and tuning, tedious but not hard,
it's worth 5-10 peak horses separate from the rest of the tune and an MpG or two