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

 

[blown240]

thanks!

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?

I have a OBD to USB adapter. I think its called Canable or something like that.

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

Ya, I can drive with out stopping for sure. The AC cutting out doesnt matter if im in stop and go, on the freeway, or regular arround town conditions. The fan clutch was replaces about 30k miles ago, but Would be good with E fans too.

 

[Marky Dissod]

AC cutting out doesnt matter if im in stop and go, on the freeway, or regular around town.

If the AC manages to cut out on the freeway, then what kind of fan(s) you have or how many is irrelevant.

 

[TJ Baker]

I have a OBD to USB adapter.

I have several OBDII to Bluetooth adapters that I usually use mostly.

For fun I built an Arduino SAE J1850VPW to USB project for adding in custom sensors.

Here's a look at some data I grabbed today ... This is from the Car Scanner ELM OBD app...

 

[nonickatall]

Why so complicated? The system works like this: a compressor, controlled by a ac control unit, creates pressure differences in the refrigerant. These differences, combined with the condenser and expansion valve, lead to temperature differences.

This temperature difference in the refrigerant is transferred to cold air using a heat exchanger. This cold air is then used by the air conditioning system, with the help of the climate control unit, a fan, and a flap control system to cool your interior. The system is relatively complex.

So we're dealing with a system that basically has two circuits.

To diagnose the fault, it's a good idea to first check if system 1, namely the compressor and refrigerant, is working properly. You can easily test this by hand.

If your system suddenly stops delivering cold air while you're on the freeway, open the hood and feel the high-pressure and low-pressure lines.

One should be ice-cold and the other lukewarm. If this is the case, your problem lies somewhere in the controller or with the accumulators. If not, your problem lies somewhere in the compressor circuit, with the refrigerant, or with the magnetic clutch.

If your air conditioning lines aren't getting cold, for example, it could be that you have water in the system. After the air conditioner has been running for a while, this water freezes at the expansion valve and prevents the system from continuing to operate.

Therefore, once again, if your system suddenly stops cooling, continue driving a few miles, get out of the car, touch the air conditioning lines and tell us what the result is.

 

[KerryBoehm]

Sorry if I missed it but have you actually measured the high and low side AC pressures? I'm not talking with the gauge on the AC Pro can but an actual AC gauge set? That's where you want to go first. Especially the age of the vehicle. 20 years old my first suspicion would be a leak. Actually, my second and third suspicion would be that too

 

[EddieC]

This is from left field and may have no bearing but Subaru's ac clutch has a specified gap range between the face plate and the main body. Apparently as there is wear the gap widens. The face plate is originally installed with a few shims to get the original spec'd gap when new.
Some have reported that when their systems don't properly engage when it is very hot out the and found to have too wide a gap the issue was addressed by pulling off the face plate and removing a shim or two to make the gap within specs. The reports are that it solves their issue.
Our (11 year old) gap is out of range and the ac will cool to a point but when the temperature is in the 90's outside the ac clutch can quit engaging after a while.
I am going to give the easy fix a try rather than replacing the entire unit.

So this may or may not be applicable in some way.
Good luck.