AC Clutch

jerry d · May 30, 2005

My 1997 Tahoe started blowing warm air out of the ac, so I added some 134a to the system, and that seemed to fix the problem. Now it seems that my clutch is always engadged. I thought it should kick off and on while the ac is running? Am I wrong, or do I have another problem?

vhato · May 30, 2005

My 1997 Tahoe started blowing warm air out of the ac, so I added some 134a to the system, and that seemed to fix the problem. Now it seems that my clutch is always engadged. I thought it should kick off and on while the ac is running? Am I wrong, or do I have another problem?

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Nahh, It may not need to cycle off. You are just fine. If you overcharged it, it would shut off or blow the excess out anyway.

BBSilverado · May 30, 2005

If you overcharged it, it would shut off or blow the excess out anyway.

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NO AC system will blow the excess out, that would be against federal regulations prohibiting venting refrigerent to the atmosphere. If you overcharged it, it will flood the compressor and lock up but it will not blow it out unless it ruptures something.

jerry d · May 30, 2005

I did not over charge it, I charged it untill the guage showed it was in the blue zone, It said about 35 pounds on the guage. I am just wondering about the clutch cycling, or lack of cycling in my case?

vhato · May 30, 2005

If you overcharged it, it would shut off or blow the excess out anyway.

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NO AC system will blow the excess out, that would be against federal regulations prohibiting venting refrigerent to the atmosphere. If you overcharged it, it will flood the compressor and lock up but it will not blow it out unless it ruptures something.

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What?? Then why do many vehicles hav pop off valves mounted right to the compressor. My girlfriends 2000 mustang was overcharged by a shop because she wanted the Ultra-Cool stuff and it blew the exess right out.

BBSilverado · May 30, 2005

I did not over charge it, I charged it untill the guage showed it was in the blue zone, It said about 35 pounds on the guage. I am just wondering about the clutch cycling, or lack of cycling in my case?

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Low or no compressor cycling is caused by either a faulty pressure switch or an undercharged system. I would say your system is still undercharged. you added enough for it to start cooling but not enough for it to ever reach the high pressure cutoff switch.

as for venting that Vhato mentioned, here is the EPA reg. on venting.

You may be right, but I have never seen a blow off valve on any AC system.

The Prohibition on Venting

Effective July 1, 1992, Section 608 of the Act prohibits individuals from knowingly venting ozone-depleting compounds (generally CFCs and HCFCs) used as refrigerants into the atmosphere while maintaining, servicing, repairing, or disposing of air-conditioning or refrigeration equipment (appliances). Only four types of releases are permitted under the prohibition:

"De minimis" quantities of refrigerant released in the course of making good faith attempts to recapture and recycle or safely dispose of refrigerant.

Refrigerants emitted in the course of normal operation of air-conditioning and refrigeration equipment (as opposed to during the maintenance, servicing, repair, or disposal of this equipment) such as faulty equipment and leaks. However, EPA requires the repair of leaks above a certain size in large equipment (see Refrigerant Leaks).

Releases of CFCs or HCFCs that are not used as refrigerants. For instance, mixtures of nitrogen and R-22 that are used as holding charges or as leak test gases may be released, because in these cases, the ozone-depleting compound is not used as a refrigerant. However, a technician may not avoid recovering refrigerant by adding nitrogen to a charged system; before nitrogen is added, the system must be evacuated to the appropriate level in Table 1. Otherwise, the CFC or HCFC vented along with the nitrogen will be considered a refrigerant. Similarly, pure CFCs or HCFCs released from appliances will be presumed to be refrigerants, and their release will be considered a violation of the prohibition on venting.

Small releases of refrigerant that result from purging hoses or from connecting or disconnecting hoses to charge or service appliances will not be considered violations of the prohibition on venting. However, recovery and recycling equipment manufactured after November 15, 1993, must be equipped with low-loss fittings.

toyotatech · May 31, 2005

Vhato is right about the over pressure valve. Look on the compressor, it's there. If you did not have one the compressor would have the potential to explode sending shrapnel everywhere. (Talk about a recall) When they talk about venting, they mean when servicing the system. In the old days, you would simply disconnect a line or remove one of the schrader valves and let it out. Now we use expensive recovery machines. Also, on most GM systems, if the charge is low it will cycle faster.

jerry d · May 31, 2005

ok, I am no mechanic, so I want to understand this. The reason my clutch is staying engadged all the time is because my system is still low on freon? It sure would be less expensive if all I needed to do was add more freon, verses a trip to the shop, but I dont want to mess it up by adding more???

toyotatech · May 31, 2005

ok, I am no mechanic, so I want to understand this. The reason my clutch is staying engadged all the time is because my system is still low on freon? It sure would be less expensive if all I needed to do was add more freon, verses a trip to the shop, but I dont want to mess it up by adding more???

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Was the system completely empty when you charged it? Is the system blowing cold air now? How much R134A did you add?

jerry d · June 1, 2005

The system was blowing warm air, the guage showed it in the green, I dont remember the poundage before I added the 134a to it. I had to add about 20oz to get the dial in the blue range at 35 pounds. It is now blowing nice and cold, but my clutch is staying engadged all the time. I thought it should cycle off and on? Or is the clutch always engadged when it is operating properly?

toyotatech · June 1, 2005

The system was blowing warm air, the guage showed it in the green, I dont remember the poundage before I added the 134a to it. I had to add about 20oz to get the dial in the blue range at 35 pounds. It is now blowing nice and cold, but my clutch is staying engadged all the time. I thought it should cycle off and on? Or is the clutch always engadged when it is operating properly?

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It should cycle on and off. If you go out on a cool morning, it should cycle on and off more than it would on a hot humid day. As the evaporator temperature reaches 30-32 degrees F, The temp sensor in the evap cycles the compressor off. This is what keeps the evap in the dash from turning into a block of ice.

If the system was empty,it had air and moisture in it. You need to pull a vacuum on the system for 20 minutes to get the air out and boil the moisture out. If you just put r134a in, your pressures will be high. This may be affecting your compressor cycling.

Too much r134a will also cause this. You know it has a leak somewhere because it was low. Maybe you should just drive it and see if the compressor starts cycling as the charge diminishes.

The right way to fix it is to find the leak, fix it, and pull a vacuum and put the correct amount of r134a in it. The amount to charge is on a sticker under the hood. Hope this helps.

jerry d · June 2, 2005

The system was blowing warm air, the guage showed it in the green, I dont remember the poundage before I added the 134a to it. I had to add about 20oz to get the dial in the blue range at 35 pounds. It is now blowing nice and cold, but my clutch is staying engadged all the time. I thought it should cycle off and on? Or is the clutch always engadged when it is operating properly?

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It should cycle on and off. If you go out on a cool morning, it should cycle on and off more than it would on a hot humid day. As the evaporator temperature reaches 30-32 degrees F, The temp sensor in the evap cycles the compressor off. This is what keeps the evap in the dash from turning into a block of ice.

If the system was empty,it had air and moisture in it. You need to pull a vacuum on the system for 20 minutes to get the air out and boil the moisture out. If you just put r134a in, your pressures will be high. This may be affecting your compressor cycling.

Too much r134a will also cause this. You know it has a leak somewhere because it was low. Maybe you should just drive it and see if the compressor starts cycling as the charge diminishes.

The right way to fix it is to find the leak, fix it, and pull a vacuum and put the correct amount of r134a in it. The amount to charge is on a sticker under the hood. Hope this helps.

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Thanks for the help, I am taking it to the shop friday.

MTRMAN5 · June 2, 2005

JERRY D TRY THIS, WITH THE A/C ON RECIRCULATE PUT THE BLOWER ON LOW SPEED, AND SEE IF AFTER A FEW MIN. THE COMPRESSOR KICKS OFF, THE LOW SIDE PRESSURE SHOULD START TO GO LOWER, FROM WHAT YOU SAID 35 TO MAYBE 25 OR LOWER, AT THIS TIME THE LOW SIDE SWITCH WILL OPEN SHUTTING OFF THE COMPESSOR, WHEN THE LINE PRESSURE RISES THE COMPRESSOR WILL TURN ON AGAIN, THIS KEEPS THE EVAPORATOR FROM FREEZING UP. IF NOT ADD ONE CAN OF 134, TEN OF SO OZ. TELL ME THE OUTSIDE TEMP AND HUMIDITY I MAY BE ABLE TO HELP WITH MORE INFORMATION. ALSO ALL COMPRESSORS HAVE A POPOFF VALVE ON THE REAR OF THE COMPRESSOR FOR OVER CHARGING AND WILL OPEN IF THE HIGH SIDE PRESSURE GETS AROULD 350 PSI OR SO..I HAVE SEEN SOME OPEN AT 400 OR MORE. WHEN THIS HAPPENS IT WILL GET YOUR ATTENTION, AND THAN CLOSE AFTER IT PURGES THE EXTRA....ABOUT A SPLIT SECOND...

.MTRMAN5.

jerry d · June 2, 2005

JERRY D TRY THIS, WITH THE A/C ON RECIRCULATE PUT THE BLOWER ON LOW SPEED, AND SEE IF AFTER A FEW MIN. THE COMPRESSOR KICKS OFF, THE LOW SIDE PRESSURE SHOULD START TO GO LOWER, FROM WHAT YOU SAID 35 TO MAYBE 25 OR LOWER, AT THIS TIME THE LOW SIDE SWITCH WILL OPEN SHUTTING OFF THE COMPESSOR, WHEN THE LINE PRESSURE RISES THE COMPRESSOR WILL TURN ON AGAIN, THIS KEEPS THE EVAPORATOR FROM FREEZING UP. IF NOT ADD ONE CAN OF 134, TEN OF SO OZ. TELL ME THE OUTSIDE TEMP AND HUMIDITY I MAY BE ABLE TO HELP WITH MORE INFORMATION. ALSO ALL COMPRESSORS HAVE A POPOFF VALVE ON THE REAR OF THE COMPRESSOR FOR OVER CHARGING AND WILL OPEN IF THE HIGH SIDE PRESSURE GETS AROULD 350 PSI OR SO..I HAVE SEEN SOME OPEN AT 400 OR MORE. WHEN THIS HAPPENS IT WILL GET YOUR ATTENTION, AND THAN CLOSE AFTER IT PURGES THE EXTRA....ABOUT A SPLIT SECOND...

.MTRMAN5.

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I tried what you said about the recirculate button, and it did cycle. I hope that means everything is working the way it should. It does blow very cold air now.