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A/C circuit design

jacobyjas on Sun September 21, 2008 4:35 PM User is offline

Year: 1996
Make: Toyota
Model: Corolla
Engine Size: 1.6
Refrigerant Type: R134a
Country of Origin: United States

I'm helping my son repair the A/C on his girl friend's Corolla. I don't see any suction-side accumulator/drier and I don't see a restriction orifice or throttle valve. The compressor and clutch were replaced with a rebuilt in July (by my son and me) and since then the clutch melted down about a month ago. We pull the compressor off this morning. The compressor turns ok and when I put my finger over the discharge port, it builds pressure with I turn the shaft. The clutch electromagnet circuit is shorted and shows clear evidence that it got hot (the insulation is extruded out around the periphery).
When I blow air through the hoses, they show no signs of excessive restriction and no indications of black death.
When I blow air into the compressor discharge hose (compressor removed) there is some restriction, but not blockage. Using a 120 psig compressor capable of about 8 cfm, I show about 70 psig on the discharge and 0 on the suction (suction is open to atmosphere). This seems like a reasonable pressure drop.
The compressor has a warranty, but I'm trying determine if there is something that caused the clutch to fry. The discharge pressure was normal when we charged it back in July when we replaced the compressor.
Does anybody know what Toyota uses for dropping the refrigerant pressure and if they use any kind of an accumulator/dryer?

bohica2xo on Sun September 21, 2008 5:02 PM User is offline

Your Toyo is a TXV system, and it has a receiver/dryer - which should have been changed with the compressor.

1996 Corolla receiver / dryer

1996 Corolla expansion valve

As for the failed clutch, overheating can come from a shorted coil, or a slipping clutch - hard to say where the heat came from without careful examination.

TRB: Edited the extra http out of the links.

"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Sun September 21, 2008 at 7:06 PM by Automotive Air Conditioning Information Moderator

iceman2555 on Sun September 21, 2008 5:56 PM User is offlineView users profile

This is a TXV/Rec/Drier system. The Rec/drier/filter is located on the driver side of the vehicle in front of the condenser. This is on the liquid line as it exits the condenser. The TXV is located on the evaporator located in the air plenum box in the dash.

The statement was that the compressor was exchanged, however, nothing was mentioned concerning the TXV, and flushing the system. Knowing that the Rec/Drier/Filter was not located informs that this was not replaced as part of the repair. Also no mention of the amount of lubricant added to the system. There are several factors that may have contributed to the clutch failure.
The foremost question....why was the compressor changed? What type of failure occurred?

If the compressor was replaced due to a 'burned clutch' also...then we simply have a repeat failure and a system that was not completely evaluated post compressor replacement. The down side of this compressor installation is the adding the compressor with an unknown quantity of lubricant and failing to properly prepare the system for the new compressor adds many new parameters to the repair/compressor replacement.

Without knowing how much lube was we have an unknown factor of the total amount of lube in the system. How was the system recharged...the use of correct equipment or simply adding refrigerant until a certain pressure point was obtained? This at best is a 'guesstamation' for the best of techs....almost an impossibility for the average DIYer. A refrigerant recharge of 1.54 lbs (24.64 oz) is very difficult to obtain simply by charging by pressures. An undercharge of 10-15 % may result in serious compressor damage. The issue is clutch burn out....this may be a result of loss of lubricant flow to the compressor resulting in an increase in internal friction....the compressor beings to 'bind internally' and the clutch begins to slip....and slip....and of course the resultant heat destroys the clutch....similar to the description in the post. The fact that the compressor rotates by hand is not a true test that during operation that internal binding was not occurring.

The fact that air can be blown thru the condenser (compressor discharge line) does not indicate a fully functioning condenser. If the compressor was replaced due to a possible noise issue...or it was locked up there is very good probability that the condenser is history. There is not mention of an attempt to flush and clean this vital part. A restriction in this area will result in a drastic increase in discharge pressures and will result in possible compressor damage...or once more...the slippage factor becomes evident and the burned clutch results.

Nothing was mentioned concerning a test of the clutch/compressor electrical. How much voltage is available at the clutch...what is the restriction of the new clutch...although at this point that issue is mute. Low voltage....a bad ground...excessive coil restriction will also result in possible clutch slippage.....excessive heat.....and you already know the end result.

Also, it is possible for an engine cooling system problem (excessive high side pressures) may result in a 'burned' clutch also. Insure that the engine cooling system is fully operational. Esp the fans.

Unfortunately, at this point, we must return to basics.

If this were in my shop.
1. Recover the refrigerant.
2. Remove the evap/txv...completely flush the evap to remove all lubricants. A suggestion would be to replace the TXV although this may not be entirely necessary. Simply a CYA move at this point. Lubricant may be added to the evap prior to re installation into the vehicle.
3. Replace the Rec/Drier/Filter. Add no more than 1/2 to 1 oz of lube to the drier.
4. Flush the condenser....a better suggestion would be to replace the unit. There is very little chance that the average DIYer will be able to test a condenser to determine if it is indeed restricted.
5. Replace the compressor/clutch assembly. Although the clutch seems to be the only failed is part of the warranty for the compressor. Insure that the compressor is lubed properly.
Normally add app. 25-30% of system lubricant charge to the compressor. This should be a Denso 10PA15C compressor and they are very easy to rotate by hand to insure pre installation lubrication.
6. All lines would be flushed to remove any possible residual contamination.
7. Reinstall all components using new orings....the use of a thread/oring sealer similar to Nyloq is good...or at least lubricant the threads and orings with mineral lube...not PAG or POE..use mineral lube on these parts.
8. Evac and recharge the system to to use a calculated recharge machine to insure that the correct amount of refrigerant is added to the system
9. Prior to compressor engagement...test the compressor electrical system. A min of battery voltage to the clutch coil. Coil resistance should not exceed 3.5 ohms.

Hopefully the condenser has been changed as part of this repair...if not the only true test of flow is a temperature drop test between the inlet and outlet. Look for a temp drop around 25-28 degrees.
Excessive temp drop is an indication of a restriction....too little drop normally indicates a possible engine cooling system problem.

Since the compressor was only functional for a short period of time...July to bet would be on an undercharged system. This could be the result of a initial undercharge or a possible leak in the system. This resultant undercharged allowed for insufficient lubricant flow and the compressor began to bind inside. This lack of lubricant flow to the compressor may also be the result of a restriction in the condenser inlet...resulting in insufficient refrigerant flow for the compressor and a drastic increase in discharge pressures (between the compressor and condenser). If the compressor is removed and less than 1- 1.5 oz is removed from the cast....this would be a good indication of lack of lubricant flow.

Good luck with the repair.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

jacobyjas on Sun September 21, 2008 5:57 PM User is offline

Thanks. I found the receiver/dryer up in front of the condenser, but I don't see the expansion valve anywhere under the hood. Is it under the dash?


mk378 on Sun September 21, 2008 6:40 PM User is offline

Yes it is inside the evaporator box. The box can be removed without taking the whole dash out. Remove the glove compartment by unscrewing the hinges. Disconnect the refrigerant lines under the hood and then remove the evaporator box through the glove compartment hole.

jacobyjas on Sun September 21, 2008 8:05 PM User is offline

Wow, thanks for the time you spent on this reply... I'll address the unknowns for which I have answers.
The original compressor was replaced because the clutch was fried and the compressor was locked up. I did not disassemble the old compressor, so I'm not sure about the extent of the internal damage. The ports were shiney clean; no signs of black death. The insides of the hoses also appeared to be clean. The oil that came out of them was very light amber colored. I assumed the failure of the original clutch was due to the compressor locking up.
I drained the oil from the old compressor and low pressure refrigerant lines into a graduated container. I put that much new oil back into the compressor and suction line.
I did check the voltage to the clutch. The clutch fuse was blown, probably due to the failure of the original clutch. The open circuit voltage was about 13 volts once a new fuse was installed.
Several years ago I built a knife-edge balance scale for dispensing refrigerant. It has a couple of slings on each side. One side holds the bottle of refrigerant, the other side a five gallon bucket into which I put water. Once I get the bucket full of enough water to balance against the weight of the refrigerant bottle, I remove the volume of water equivalent to the weight of refrigerant that I want to add to the system. Then when I'm charging the system, I close the valve when I see the balance return to center. I suppose this could be off a little due to the difference in the density of water at the ambient temperature, but that can't be more than a percent. I've used this set up on at least a dozen recharges without problems.
From my notes, the ambient that day was 94 F and the discharge pressure was about 265 psig. The cooling fan was running.
Since the condenser for this car is so cheap, I'll take your advice and replace it. Same for the expansion valve, once I find it. I'll also carefully check out the electrical side of the clutch to determine whether or not the clutch force was inadequate (leading to slippage).
Thanks again for the time you spent responding to my post.

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