Intermittent A/C very cold and then warm

[OR VietVet]

Attached gauges at shop for intermittent a/c problem. This is the same 2005 Tahoe I did the exhaust manifold clamps on recently. Drove to pick her up and was ice cold and 1/2 way there, started blowing warm till got to her house. Shut off. She got in. Drove back to my house and a/c worked the whole way.

At shop today.....Ambient temp at 84 degrees.....29 degrees out the vent..... low pressure at 25 psi and high pressure at 200 psi.....system working normal..

Found 2 history codes: B0408-Temperature Control 1 Circuit Malfunction & B0418-Temperature Control 2 Circuit.

 

[Tonyv__]

Any history on the compressor itself? And not sure if you could hear it while driving. Was the compressor engaging when warm?

My compressor was intermittent last summer. It eventually got worse and one day when it wasn’t engaging, I tapped the clutch with a hammer. Engaged immediately and worked fine when it was engaged. I chalked it up to a failing clutch.


Replaced compressor and it’s been cold so far this summer

 

[OR VietVet]

No odd noises from compressor and clutch cycled as should. This is a manual control a/c unit. When system malfunctions, I need to catch it and see if clutch is engaged or not.

Going to do further inspection at my house.

 

[Tonyv__]

No odd noises from compressor and clutch cycled as should. This is a manual control a/c unit. When system malfunctions, I need to catch it and see if clutch is engaged or not.

Going to do further inspection at my house.

Yeah catching it was the tough part. It would work fine for days then randomly start to get warm while driving.

I was always in sketchy neighborhoods or busy roads so I wasn’t thrilled to pull over and leave it running while I crawled under the van to try and .

Finally caught it acting up in a parking lot and checked it out immediately.

 

[OR VietVet]

I can use your help again. Has the manual heater-a/c control head in the dash with rear defogger on it and has the CJ3 RPO code.

I am looking for the Genuine GM or AC Delco part numbers for that control module and the actuator that controls the hot/cold mode. VIN is 1GNEK13T45R142468.

Her a/c can be ice cold and while driving will go to warm, without touching temp controls. When I run it, I can change the temp controls and can hear a loud ratcheting noise as the actuator change positions and sounds like is behind the glove box area. I believe the actuator is failed/failing and the control head has problems because the system is full and when it turns warm, the a/c clutch is disengaged and jumping the low pressure cycling switch does not engage the clutch. The ratcheting noise has been going on for quite a while, even though the a/c would blow cold. Now the noise is still there and the signal is not even at the low pressure switch at the accumulator I tried crossing the connections and still no clutch engagement. The other actuator controls for the modes of blowing out of dash, floor, both or defrost, all work for the direction of flow. When those are operated there is no ratcheting noise.

 

[Fless]

I can use your help again. Has the manual heater-a/c control head in the dash with rear defogger on it and has the CJ3 RPO code.

I am looking for the Genuine GM or AC Delco part numbers for that control module and the actuator that controls the hot/cold mode. VIN is 1GNEK13T45R142468.

Her a/c can be ice cold and while driving will go to warm, without touching temp controls. When I run it, I can change the temp controls and can hear a loud ratcheting noise as the actuator change positions and sounds like is behind the glove box area. I believe the actuator is failed/failing and the control head has problems because the system is full and when it turns warm, the a/c clutch is disengaged and jumping the low pressure cycling switch does not engage the clutch. The ratcheting noise has been going on for quite a while, even though the a/c would blow cold. Now the noise is still there and the signal is not even at the low pressure switch at the accumulator I tried crossing the connections and still no clutch engagement. The other actuator controls for the modes of blowing out of dash, floor, both or defrost, all work for the direction of flow. When those are operated there is no ratcheting noise.

Maybe we should ask @915_Tahoe

 

[OR VietVet]

I did and gave him the whole story but I copied it here to see if the electrical/mechanical problems ring a bell with anyone.

She showed up today with it ice cold and while I was doing a live data search and she moved the hot/cold slides, it started staying hot/warm. I tried a reset and no help and like I said, there was a ratcheting noise at the glove box area when moved the hot cold slides but no noise when changing the modes for direction control.

 

[OR VietVet]

@Fless, IIRC you laid out the locations of the actuators and what they were for, at least on the GMT800 series.

Mode door actuator is above the gas pedal.

D/S hot/cold actuator is center area above the transmission hump.

P/S hot cold actuator is under dash cover above the glove box and to the left of the heater core hump at top of HVAC box.

Recirc actuator is under dash cover and to the right and at the firewall area of the HVAC box.

 

[OR VietVet]

This morning I swapped the A/C compressor relay with the horn relay and still was able to duplicate the problem. I then removed the a/c relay and jumped from pin 30 to pin 87 and the compressor came on and stayed on and the temp control went from cold to hot and back, as the temp control levers were moved. IMO, the control head in dash is the culprit of her problems.

 

[Fless]

@Fless, IIRC you laid out the locations of the actuators and what they were for, at least on the GMT800 series.

I didn't.

 

[OR VietVet]

Do you remember who did? I think I am right but would like to hear some confirmation.

 

[Fless]

AFAIK @swathdiver has indicated some on the later models, but I don't know who on the NBS ones. Not sure if they're similar or not.

 

[OR VietVet]

Well then, I think I heard it that way someplace and hope to hear from @915_Tahoe and he will confirm.

 

[swathdiver]

Pretty sure this also applies to the 800s with CJ2.

I believe the CJ3 system uses some different part numbers.

 

[OR VietVet]

Pretty sure this also applies to the 800s with CJ2.

View attachment 465349

I believe the CJ3 system uses some different part numbers.

In this case, the 89018365 actuator, is what I have found for the P/S air temp actuator and CJ3 manual control head.

 

[OR VietVet]

Plus, my codes I had to work with were B0408 and B0418.

 

[nonickatall]

I'm pretty sure your problem is with the actuator on the driver's side.

I had the same problem with my truck. At some point during a long trip in very hot weather, hot air suddenly came out on the driver's side. It didn't last long, and then cold air suddenly came back. This happened a few times, and then suddenly only hot air came out.

I then replaced the actuator responsible for the driver's side, which is the one located behind the center console.

The problem hasn't occurred since then...

These little units are stepper motors which knew their position with a potentiometer. If this potentiometer starts to fail, the HVAC unit identifies a false position, of the blend door and starts to get nuts...

 

[OR VietVet]

I'm pretty sure your problem is with the actuator on the driver's side.

I had the same problem with my truck. At some point during a long trip in very hot weather, hot air suddenly came out on the driver's side. It didn't last long, and then cold air suddenly came back. This happened a few times, and then suddenly only hot air came out.

I then replaced the actuator responsible for the driver's side, which is the one located behind the center console.

The problem hasn't occurred since then...

These little units are stepper motors which knew their position with a potentiometer. If this potentiometer starts to fail, the HVAC unit identifies a false position, of the blend door and starts to get nuts...

She can, or I can, turn on a/c and it will blow cold on both sides or hot on both sides if not working. It never blows hot or cold on one side and the other side is the opposite. It can be on cold and while driving it will start to blow warm on both sides. It can either then go back to cold after driving for a while or back to cold on a restart. It is never one side or the other. When it works or problem happens, it effects both sides at same time. Based off of the codes I got and procedures with the a/c relay, I am convinced it is the control head in dash. The P/S temp actuator makes a ratcheting noise but does switch when prompted. When system is blowing cold and then goes warm, the a/c clutch is not activated. If the problem occurs and I force the a/c clutch, by jumping relay, the cold come back.

 

[nonickatall]

She can, or I can, turn on a/c and it will blow cold on both sides or hot on both sides if not working. It never blows hot or cold on one side and the other side is the opposite. It can be on cold and while driving it will start to blow warm on both sides. It can either then go back to cold after driving for a while or back to cold on a restart. It is never one side or the other. When it works or problem happens, it effects both sides at same time. Based off of the codes I got and procedures with the a/c relay, I am convinced it is the control head in dash. The P/S temp actuator makes a ratcheting noise but does switch when prompted. When system is blowing cold and then goes warm, the a/c clutch is not activated. If the problem occurs and I force the a/c clutch, by jumping relay, the cold come back.

I see you point.

As I remember in my case it was also that shortly came hot air on both sides. Probably when HVAC is on auto that both temperature actuators move the same.

That the compressor is not engaged is strange. Probably when the system thinks that actuators are full warm, the compressor is turnt off shortly, to save fuel or prevent icings conditions on the expension valve...

But when your actuators make noise it's very likely that the problem comes from that.

It easy to change the actuator in the passenger foot space. So use a used one to check if it helps.

If not the solution, I would change the HVAC for test purpose...

 

[OR VietVet]

The temp actuator, for the ratcheting noise one, is the temp control actuator for the passenger side and that is the PITA one under the dash cover. The temp one for the driver's side is the one that is just above the transmission hump and accessed from passenger floorboard.