FRENCH MEMBER IN TROUBLE WITH HVAC

[Serge PETIT]

Its not a Crew Cab with it's the same on my 2000 4x4 , 4,3l , 4 doors , Automatic Blazer which has trouble with the automatic AC .
Even when AC is switched off the compressor keep engaged and continue to produce cool air .
It seems that the compressor clutch is always engaged ( not noise of the clutch engaging and disengaging .
The accumulator is icy and no condensation leak on the passenger floor
I have controled the fuses and they look good .
What can it be ?
Not enough gas in the system ?
The relay which stay sticked ?
Thanks in advance for your ideas because it's not here in France that I will get some !
Serge

[Jongo88]

It is most likely the low pressure switch. Some call it a cycle switch. It is on your accumulator tank. There is a shrader valve under the switch so when you change it you won't loose your freon.

This is a very common problem and a very easy fix.

[HenryJ]

Agreed. Pull the wiring connector and see if the compressors clutch disengages.

[Jongo88]

Here is what it looks like.
http://www.google.com/imgres?imgurl=htt ... s%3Disch:1

[HenryJ]

Located on the filter / dryer (dehydrator) just outside the HVAC housing in the engine compartment.

If it does not stop when you unplug it , then suspect a stuck relay.

[Serge PETIT]

Thanks for very fast answers .
I will check that switch and keep you informed .
I don't think its a relay because I just have inverted the HVAC relay with another and it changed nothing ..............
Serge.

[Serge PETIT]

I just made the test and when the sensor is unplugged the clutch stay engaged .
When disconnecting the connection on compressor it disengage same when I disconnect the relay .
After less than 2 minutes the filter/dryer was covered with ice .........?
Anay other suggestion ?
Serge.

[HenryJ]

The auto climate control is a wild card here with which I am not well versed. Are you saying that the compressor runs even in the vent position where no AC is used? (AC is used in the AC positions and defrost positions)

With the low pressure switch unplugged there should be no engagement of the AC system. An open circuit there should disable the system. Follow those wires and look for something pinched or shorted.

Try disconnecting the high pressure switch on the back of the compressor. That too should disable the system. That one would not keep it running though.

[Serge PETIT]

The compressor is always running even when the touch AC on the dash climate control unit is not pushed and the light on this touch is off .
Something disconnected behind this climate control unit ?

[HenryJ]

Just trying to isolate it as a control problem at the selector or a problem elsewhere. Those selector assemblies are not cheap.

[Serge PETIT]

As you have suggested , I have disconnected the low pressure switch and the clutch stay engaged !....................
I will try tomorrow to control all the connections behind the "climate control unit of the dash before trying a change (perhaps for a used part from S10 Warehouse ? is it a good thing ?) .
Will keep you informed .
Serge .

[HenryJ]

Used would be a good idea.

What has me worried is that disconnecting the low pressure switch did not disengage the clutch. It should have.
The low pressure switch is easy to test. Check for continuity with it installed. With it installed and pressure against it it should be a closed circuit. Then remove it and once the pressure is relieved the circuit should be open.

Here is the circuit:
Selector switch > High pressure switch > low pressure switch > clutch

If the high pressure switch is open the low pressure switch will not receive power and neither will the clutch. If the low pressure switch is open the clutch will not receive power.
See why I question it working with the low pressure switch disconnected? For that to be the case there must be a short circuit somewhere.

[blaz]

Is it possible that the clutch is just seized together? If the clutch is not being effected by any of the sensors. My first check would be to remove the belt and disconnect the battery and see if you can turn the pulley.

[HenryJ]

Good point. I though it did stop when he disconnected the wires at the clutch though?

[Serge PETIT]

When I have pulled out the relay with engine running The clutch has disengaged .
It make me think that the clutch is not seized .
I think it's more electrical because the compressor keep running even when the AC is switch off at the climate controle module .
Thanks to Blaz for the suggestion .

[Serge PETIT]

I have discovered in the Rockauto catalog in the A/C pages that a sensor placed on the dash is called "Climate control sun sensor"

2000 CHEVROLET BLAZER 4.3L 262cid V6 FI (W) OHV : Heat & Air Conditioning : Climate Control Sun Sensor Wiki Price
ACDELCO Part # 1572446 More Information About this Part {#15740822}
SENSOR,SUN LOAD TEMP

Part Image
* Non-stock item--shipping delayed up to 5 business days

But no information in the wiki .
Is that sensor in connection with the compressor to be engaged or not ?

[Serge PETIT]

I am just back from my parking lot where I have made the tests .
Results are :
1) low pressure sensor disconnected ..........Clutch engaged and compressor running
2) high pressure sensor disconnected...........Clutch engaged and compressor running
3) HVAC relay in the engine compartement fuse case pulled out ........clutch disconnected and compressor off
4) Clutch coil disconnected ......................clutch not engaged and compressor off
5) Automatic Climate Control module on the dash:
- AC switch off (no light) clutch engaged and compressor on
- ACswitch on (light on) clutch engaged and compressor on
I think we may consider that the compressor clutch is fonctioning right .

All fuses for A/C are OK .
I have checked the automatic AC control module connector......nothing special or disconnected

I think that now I have to check the "freon" in the circuit because I am surprised by the fact that the dry/evaporator is covered with frost in one minute !
If "freon" is normal I think that I will have to change the HVAC control module because a componant may have failed (?) even if ventilation , defrost, air recycling and all contactors positions are fonctionning .........

At the moment it's not very hot in France (around 75 °F) and I have no long travel planed so I have disconnected the coil of the clutch and will reconnect if necessary .

Any new opinions/ suggestions ?

Thanks for for your help .

[HenryJ]

Check the connections at the PCM. The DK GRN/WHT wire to the AC compressor clutch relay comes from the PCM. Look for short to ground in that wire. You have a problem there somewhere.

The PCM receives a signal from the selector switch requesting AC. If the low pressure switch is closed indicating enough pressure and the high pressure switch is closed indicating no excess in pressure the PCM sends a signal to the clutch relay to start. The Electronic climate control module can also send a signal to the PCM requesting AC activation. This also must come through the high pressure switch.

What you have indicated is that the relay for the AC is grounded / activated all the time regardless of the selector switch, high pressure switch and low pressure switch. I assume you have already swapped the AC relay and confirmed that it is working properly and no stuck? If the relay is functioning properly, then this leads me to believe that either the request wire has a short to ground or the PCM has a problem.

Test both ends of that wire for a short to ground with the connector removed from the PCM and the relay removed from the electrical canter. If it is OK, the PCM is all you have left.

[Serge PETIT]

Thanks Brule . I have not checked that point so I will do on monday now and keep you informed . Have a nice week-end .

[Serge PETIT]

After long search on Internet , I think that there is a point we have not enough considered .
It's the frozing of the drier and of a pipe on compressor a soon as it has started running .
From what I have read it may come from a excess of moisture in the drier blocking the liquid and making a to low temperature (freeze) and a flood back in compressor which compromise the thermostatic regulation for the coil .
So We will start by flushing the circuit changing the drier and the liquid and see what happen .
I have to say that the last change of the liquid has been made in July 2007 . and that during the cold periods iI have never started the AC system as recommended !!!!! Certainly a lot of moisture in the circuit !!!!!
Will keep you updated .

[HenryJ]

An intact system should never need to be recharged or the refrigerant replaced. Moisture can not be introduced unless there is a leak.
The line freezing you mention there is internal to the system and not frozen condensation on the outside of the lines as I had been lead to understand. Condensation on the outside of the low pressure line is very normal. A very cold system at temperatures below 80F can freeze that condensation. That does not worry me. If the freezing is internal to the system, the high pressure switch would be triggered shutting down the clutch do to the blockage , or restriction.
Normally the clutch would cycle and the icing on the outside of the low pressure line would not occur. Condensation, yes, icing not so much. Right now yours is running all the time. There is no regulation.

While you could have problems internally, you do have problems externally. We have already found that neither the low pressure, nor the high pressure switches are working as they should be.
Regardless of internal conditions those must function correctly for the system to work properly.

Evacuating the system, replacing the orifice tube , filter dryer (with the correct type and amount of lubricant) , followed by pulling a vacuum on the system and recharging is not unreasonable. I do not expect it to solve problems until the systems electrical problems are resolved.

If you have access to a gauge set you can easily diagnose the condition of the refrigerant. If indeed there is an internal restriction, moisture, etc. all that would be evident by reading the high and low side pressures. Tossing a gauge set on and checking the readings is a very good idea. Any time you have problems getting gauge readings is a fantastic idea.

If you want to know more about automotive air conditioning systems, Haynes Automotive Heating & Air Conditioning Manual is a good reference. I keep one around for the charts.

[Serge PETIT]

Normaly , tomorrow afternoon I will see my maintenance guy and it is in my program to ask him to check the pressures .
So now I will go sleeping because it's 1.30 AM and tomorrow will be another day !

[Serge PETIT]

With the owner manual in hand I have test all the positions of the automatic AC control module .

I think if I well remember that normaly when button is on the front defrost position the compressor is on and the AC light on AC switch is on to .
Am I right ?

In my case the light on AC switch don't come on when on the front defrost position.

When turning the button back on the auto position the switch light come on and all HVAC flaps are moving back to the normal position (same if I place the button on an other position .

So I can say that the HVAC are correctly functioning independently of the electrical management of the compressor.

I am wondering if my failure is not here in the control module ?
meaning that the defrost electrical position is , on an "electronic point of vieuw" , stuck in the defrost position which may explain that the clutch is engage continusly ?

Will a TECH2 reader be able to check that point and give a code ?

[HenryJ]

You were unable to disengage the clutch by disconnecting both pressure sensors. Those regulate the system. There in lies a problem.

It is not likely that the TechII will have a code, but worth a shot as I have never used one and do not know all that can do.

[rlrnr53]

I have to agree with Henry J thar the problem probably lies somewhere between the relay and the clutch in the wiring.

[Serge PETIT]

Where would it be possible to find a wiring diagram . I found nothing in the haynes manual.....

[HenryJ]

The Esi Service data should have the diagrams you seek.

[Serge PETIT]

OK thanks Brule I will search .