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Weak Compressor Pages: 12

JoeFL77 on Wed September 16, 2009 2:22 PM User is offline

Year: 1992
Make: Geo
Model: Metro
Engine Size: 1.0
Refrigerant Type: r-12
Ambient Temp: 88
Pressure Low: 27
Pressure High: 206
Country of Origin: United States

I just worked on my air conditioner again and it is driving me nuts.

I'm in Central Florida so it is hot and humid. The air conditioner is intermittent. It seem to work best when it is not too hot out. I just tested it again. It worked great 3 miles to the interstate. After 7 mile on the interstate it stopped working. Vent temp went from 55 to 86. After about 4 miles it worked for 3 then quit again. didn't work fot 10 mile and started working 3 mile before I got home.

Do compressors get weak or not work intermittently? Do the valves in them "Stick" or leak?

Here what I have done so far to troubleshoot for the most recent to the oldest.

A) Today, hooked up the gauges and added 3.0 oz of R-12. Low 27 high 206. Removed blower fan motor to clean out a few leave and make sure evaporator not clogged with leaves. Only about ten in there. Worked great in the driveway. Test results above.

B) Last week. Suspected a weak clutch coil. Unable to buy a new or rebuilt clutch so I got a used compressor with a clutch and swapped it out. Same intermittent operation and a little low on cooling capacity. Suspected some refrigerant leaked while I was pulling on the hoses to changed the clutch. I heard some hissing. After I got it all together, I check for leaks and found none. I replace the refrigerant in A above.

C) 2 weeks ago. Suspected an electrical problem shutting off the compressor. Made a special box so I could select normal clutch circuit or put straight 12 volts to the clutch. Same intermittent problem with normal circuit or jumped 12v.

D) 3 weeks ago. Suspect too large an air gap in clutch. Removed one shim to bring it to .020 . Still intermittent.

E) 4 weeks ago. intermittent A/C. discovered condenser fan inop. Replaced condenser fan motor. Still intermittent.

So now I am about to buy rebuilt compressor with a new clutch. I'm thinking it it the compressor or the clutch. The engine is transverse mounted and the compressor is on the bottom so it is difficult to see it. The sight glass is easy to see. I'm considering somehow taping the gauge to the windshield and driving it but I suspect it would just show the pressures neutral when the air gets hot.

The only sensors I know that affect the clutch is a two wire switch on the high side and a mechanical switch on the gas pedal. I have played with the gas pedal switch and it seems OK.

Do you have any trouble shooting ideas?

I am leaning towards buying a rebuilt compressor and clutch. Recovering the R-12. Replacing the receiver/drier. Replacing the compressor and clutch. I was not going to touch the expansion valve since I'm too lazy to pull out all that stuff under the dash and worry about causing more problems. I was thinking about swapping to r-134 but I can save the r-12. The cars that I have swapped to r-134 were empty or had more issues than this car.

Thanks for your help,

Dougflas on Wed September 16, 2009 4:20 PM User is offline

Did you explore the possibility that THE EVAP IS freezing up? Is there a drop in airflow thru the vents? That should be a txv system and the clutch won't cycle until the evap temp gets to the freezing point.

mk378 on Wed September 16, 2009 4:57 PM User is offline

First thing is to ascertain whether or not the compressor remains engaged after the system has stopped cooling. This can be done by simply pulling over and looking under the hood. If the compressor is not engaged, put a test light on the wire to see if the car is trying to engage it.

There will be an evaporator temperature sensor to control freeze-up, it may be cutting off prematurely or not cutting off and allowing it to freeze. If there is a freeze-up, the suction line under the hood will likely be very cold and icy.

Intermittent failure of a compressor to pump is very rare unless it is a variable compressor. It appears this car is fitted with a conventional fixed-displacement compressor. To diagnose this remote possibility you'd need to watch the pressures during the failure mode.

Don't hot-wire the compressor, if the compressor ever runs without the condenser fans, you will get an overpressure and won't have the protection of the pressure switch. That usually means a blown hose.

Chick on Wed September 16, 2009 7:42 PM User is offlineView users profile

If the compressor shuts off and has power to it, you also need to check the clutch gap, could be to wide causing it to work while cool, but not engage when hot.. as well as the above comments...

Email: Chick


Freedoms just another word for nothing left to lose

JoeFL77 on Wed September 16, 2009 8:44 PM User is offline

Thanks for the help!

I went to buy a high side adapter at a AC store since the o-rings in my quick disconnect adapters are leaking. He thought it might be the expansion valve freezing up. I have not been able to look at it when it was not working. Either it starts when I get home or I am not able to look at it at the time.

The air flow is OK. There is some air leakage where the blower box goes into the evaporator box. I am going to replace the weather stripping.

I am leaning towards a malfunctioning expansion valve. On the highway going to the store the vent temp was 48 for about 10 minutes then 70 for about 5 then 48 for about 5 minutes. Then 85 for 10 minutes. It recovered and went to 48. I will stop the next time it goes to 85 and try to get the pressures. I took off the lower plastic in the wheel wheel to get a peek at the compressor clutch.

If the expansion valve is frozen I think the pressure should be very high on the high side and rather low on the low side with the suction line icy?

So forget the compressor. Now I'm thinking, recover the r-12. replace the expansion valve. recharge system. Sound plausible?

I'm driving to Miami tomorrow in another car and will resume first thing Friday.


SpinRite on Wed September 16, 2009 9:13 PM User is offline

Is it possible to use a flashlight and actually see the evaporator through any of the vents? (Might need to pull the louvers off.) Then you could "catch it in the act" while freezing up.

mk378 on Wed September 16, 2009 11:40 PM User is offline

You need to measure something, anything, while it is not working in order to narrow down the diagnosis. See if you can rig the gauges so you can watch the pressure while driving (best to have someone else drive and you just watch). This can be done by taping them to the windshield or running the hoses through the window into the car.

Blocked expansion valve will cause a very low low side (into vacuum even) and a moderately low high side. There will be no frost as there's no cooling of the evaporator. Freezing of the expansion valve usually means the system is heavily contaminated with water, simply replacing the valve won't cure that. But that's just conjecture until you measure the pressures and see if the compressor is really turning.

JoeFL77 on Thu September 17, 2009 7:53 AM User is offline

So I think I can say (pending driving with the gauges on it) that the evaporator is freezing internally not covering with ice on the outside.

It is a 17 year old car and I didn't own it for its first 100k so there could be moisture in the system from some where. Could age have caused this?

If I were to remove the R-12, change the receiver /drier, recharge it, would that maybe cure it? I could leave it on vacuum overnight. (I have a Robinair electric pump, I assume it is OK to run it on the system for 8 hours). When I recover the r-12, is there a way to purge the moisture so I can reuse it? It would be great not to tear up under the dash to change the expansion valve.


JoeFL77 on Thu September 17, 2009 7:57 AM User is offline

I know the above is speculation, but I am fairly convinced that the expansion valve is the problem. I am trying to get the cure, so I can apply it while I am still covered with grease and the tools are out.


Chick on Thu September 17, 2009 7:40 PM User is offlineView users profile

There are no short cuts to AC repair, and techs do not guess, they get the pressures when the car is cooling and when it's not. That gives us the tools to help you. speculate isn't going to cut it.. Get the gages on it and post the pressures along with the ambient temp taken at, both while cooling and when not.. When it's not, check the compressor (and lines) make sure it's running.. Hope this helps..

Email: Chick


Freedoms just another word for nothing left to lose

JoeFL77 on Fri September 18, 2009 8:24 PM User is offline

I hooked up the gauge set and drove around town up to about 45 mph. I have many reading that I will post below. It got very confusing with many readings running and idling. At first I thought it may have been low on refrigerant but after a while it seemed OK at times. I have no experience with running pressures, just idling. What I was trying to find out what the pressure was and whether the compressor was engaged when cooling failed. It was in Central Florida about 1630 so the temp was about 90F.

When the cooling failed the low was 0-5 and high was 180. I think the compressor was running at all time because the pressure changed. Low and high would neutralize. Everytime I deselected the compressor the pressure would change. Sometimes the cooling seemed modest. At the end it seemed very good.

So here are some of the pressures. idling and running.

Low High Vent Idle Running
26 240 77 X
15 150 68 X
5 150 75 X
0 150 79 X
OFF pressure balanced
15 150 70 x
6 160 73 x
5 180 75 x
5 150 76 x
15 160 67 x
20 190 67 x
0 150 80 X
Off for 10 minutes
25 230 66 x
28 260 66 x
26 230 62 x
5 150 74 x
24 170 64
0 180 77 x no cooling
of for 20 minutes
26 200 67 Inside car temp 92
18 180 59 x
19 210 62 x
21 200 55 inside car temp 85
Arrive home.

So it appears that when it stops cooling the low side is 0-5. If I shut the compressor off the low side rises to a neutral pressure.

So what do you think? I'm thinking a expansion valve problem. I was hoping that maybe changing the receiver/drier and vacuuming the system to dry it out might fix it without changing the expansion valve.

I took so many pressures that it was getting confusing. Any incite would be welcomed.


Dougflas on Fri September 18, 2009 9:11 PM User is offline

what part of central Florida are you located?

mk378 on Fri September 18, 2009 10:34 PM User is offline

Even when it does work it doesn't work very well. Vent temps should be a lot lower. Probably undercharged. If you torqued something enough to cause a leak, it's unlikely to cure itself. Check for reheating by blocking off the heater hoses. If there isn't reheating clearly the evaporator is getting nowhere close to freezing. Pressures do suggest a blocked TXV or a major freeze-up, which you can differentiate by checikng the temperature of the suction line under the hood when it stops cooling.

JoeFL77 on Fri September 18, 2009 11:18 PM User is offline

I live in Malabar, next to Melbourne in East Central FL.

As I remember the suction line was not very cool. Damp, not cold. I'll check the heater.

By major freeze up do you mean an external covering of the evaporator with ice or an internal blockage with ice because of moisture in the system? By blocked expansion valve, do you mean by some debris in the system?

To refill it, I have just added refrigerant until the pressures match the book I have. I have since bought a refrigerant scale and a vacuum pump (i used to use an air venturi one). The car has a sight glass but I wonder if air or moisture could be causing bubbles. I'm torn between recovering the r-12 and adding all new to the prescribed weight or just adding some more.

I have a MAC tools leak detector and I sniffed around and didn't find anything. I lost a little gas with the snap-on quick fitting which I have replace with a regular high side adapter. I could add a few more ounces if you don't think there is too much air or moisture in the system.


Dougflas on Sat September 19, 2009 4:30 AM User is offline

those air powered pumps are not adequate for AC work. If that is what you used, I'd recover the refrigerant,Pull a proper vacuum and use a micron gage to insure total evacuation. Charge by weight. Now you can eliminate the charge as a cause.

When I originally asked if you investigated freeze up, I was referring to the evap getting too cold and forming ice on its surface. This would cut down on the air flow coming out of the vents.

TXV freeze up is the refrigeration system having moisture in it causing the TXV to freeze shut. If you used that air powered pump, that is a good chance where your problem is located. You can borrow/rent a good pump from Autuzone. Just buy some vacuum pump oil and change the oil first. Best way to change the oil is to run the pump for 10 minutes or so, shut it down, drain the oil and refill.

JoeFL77 on Sat September 19, 2009 8:02 AM User is offline

Sorry for the confusion. In the past I have used the air powered vacuum pump on other cars. I have since purchased a electric vacuum pump. This car, the 1992 Metro, has only had 3 ounces of r-12 added by me. I bought the car about 10 years ago with 100K on it. I have not done anything to the inside of the AC system except add a few ounces of r-12. I mistakenly though the compressor clutch was bad so I have been fooling around with that for the last few weeks. The car being 17 years old and not knowing its earlier life may complicate things.

Since it seems to work normally at times, possibly a little under capacity. Am I correct in assuming that when it stops cooling, low side 0 high about 160 that it is a internally blocked expansion valve. This being an intermittent problem it may be a moisture contamination problem. Would removing the refrigerant, change the receiver/drier, and vacuuming out the system remove the moisture. Would it help to vacuum it longer, say a couple of hours, to help dry it out better? Then refill it with fresh r-12.

I'm leaving to go out of town until Monday so that is what I would like to do on Monday.


JoeFL77 on Wed September 23, 2009 7:10 PM User is offline

I worked on the system yesterday and today.

Recovered the r-12. Replaced receiver/drier. Evacuated for a long time. The oil in the vacuum pump turned milky at one point so I changed it. I read some where that is an indication of moisture. I would run the pump for 30 minutes, let it rest for 30 minutes and repeat. about 10 times. I let it settle overnight and evacuated it this AM. I added 18 oz of R-12. I worked great. Vent temps down to 42.

On the way to the airport, it stopped cooling. It lasted longer than before but was intermittent. When I return, I will drive around town with the gauges on it to confirm a blocked expansion valve.

I'm leaning toward changing the expansion valve that is malfunctioning.

I don't know why it is malfunctioning. Is it a simple malfunction due to age (17 years) or ice? Could the oil be holding enough moisture to clog it intermittently? I'm betting on a simple malfunction.


JoeFL77 on Tue September 29, 2009 4:31 PM User is offline

I just replaced the expansion valve. While filling the system, I noticed the pressures looked high and the sight glass had no bubbles after 14 oz of r-12 added. So I stopped adding r-12 figuring it is easier to add more later. Finished late last night I drove around for a little while. I seemed OK. It never lost its cooling but it was not too hot out.

One thing, while I was putting the blower box back in, I noticed the flap in the door that stops out side air had a hole in it. The door has two parts to it. A main door and a smaller door in the middle that opens out. The smaller door had an opening about 1 X 4 that had a type of foam tape weather stripping filling it. The tape had disintegrated in the middle leaving a hole. I covered it with a piece of tape on top but I am not sure the other side is sealing well. I mention this because vent temps get lower when stopped so I figure some out side air is leaking in during highway driving.

So this morning a ran up and down the highway trying to get it to stop cooling. It worked OK. Vent temps 53 to 60 running and down to 48 stopped. It wasn't great so I figured I would put the gauges on it later. Later turned out to be 4:00 PM and hot out.

Outside air temp 95 in front of condenser. Started up and got high 295 low 40 vent 62. ran about 5 minutes got 320/43 vent 57. Ran some more about 10 minutes until the cooling fan for the motor kicked on 270/43 vent 56. (note: this should not have made a difference since the radiator fan is on the left side and the condenser is on the right side). Since it was so hot out, I thought I read some where about spraying water on the condenser so I took a water bottle and squirted the condenser. The pressures dropped 190/25 vent 48. Note also that there is bubbles in the sight glass now. Could it be under charged? Those high pressures scared me so I didn't want to add more refrigerant until I talked to you all.

Also, just in case you hadn't read the earlier posts, the condenser fan was broken and I think I ran around a while with it not working. I replaced it and started on the other problems. It runs all the time now with the AC on like it should.

I am confused. Multiple problems? The new expansion valve seem to have stopped the internal blockage but is there something else. So what do you think?


JoeFL77 on Tue September 29, 2009 4:45 PM User is offline

I may have been taking incorrect readings. All the pressures are at idle. I believe that it is about 700 rpm. I read in another post that they should be taken at 1500 rpm. Does it matter?

This is a three cylinder so it is confusing using the old tool I had. I haven't adjusted the idle for years but I remember my engine analyzer having a 4/8 and 6 switch. basically take half the 8 and add 25%.


mk378 on Tue September 29, 2009 5:03 PM User is offline

Set tach to 6 cylinder mode and double the reading. For a given number of sparks you get twice as many revolutions out of a 3 cylinder as a 6. Thus the actual rpm is double what the tach says.

Edited: Tue September 29, 2009 at 5:07 PM by mk378

JoeFL77 on Tue September 29, 2009 9:35 PM User is offline

Dear MK378,

I was out playing with the car while you replied.

When I put the water previously through the condenser, I just took my squirt bottle and squirted gently into the fan and let the fan mist it through.

While you were replying, I took the hose and forcefully put some water through the condenser. I made a dramatic difference to the "dry" idle readings. So with the water going though and my wife holding the throttle higher than idle I got (with OAT about 93) 165/15 vent 42.
I let things dry out and idle for about 5 minutes and got 235/30 vent 40 (lower than before since I think it had time to cool the interior).

I believe part of my problem may have been a externally dirty condenser (17 years old). I have some foam coil cleaner in the garage ( I hope I can find it) for house AC that I might try.

Folks just arrived for dinner. I'll write more tomorrow.


JoeFL77 on Wed September 30, 2009 10:07 AM User is offline

Since forcing the water through the condenser seem to help so much, some coil cleaner might be even better.

I found the foaming AC coiler cleaner and sprayed it on the condenser. Let it set then hosed it off.

I went driving this morning. The OAT was only 79 so it may not have been a true test. The ac worked great. Vent temp between 40-43. I'll be driving this Saturday for one hour plus and it should be hot so it will be a good test.

Does it sound like a dirty condenser could have been the last problem?

Thanks, thanks, and thanks again,

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