A/C Compressor Drag

[SVX_MY_BABY]

I just had my a/c serviced and installed my original newly rebuilt OEM R12 compressor.

The system didn't cool well, if at all, after the service, so I took the Subaru R134a retrofit instructions to the tech to ensure the system was charged correctly. He evacuated the system and re-did the job as per the attached instructions. He followed them to the letter, but it still doesn't seem to be working. http://www.northursalia.com/techdocs...nt/acretro.pdf

He checked all the lines with a laser type digital thermometer and felt they were the appropriate temperature. As it was a cool day (13 Celsius) is was hard to really determine what was happening as the lowest setting on the a/c control is 18 Celsius.

I did notice that the compressor is cycling fairly frequently and at idle, which is 750 rpm, and when the compressor cuts in the rpm will drop 250 - 300-rpm to the point that the engine almost stumbles. This can't be normal.

Any help appreciated.

[huck369]

Maybe the blend door is stuck, and not letting it switch to the cool air......

[Blacky]

The rpm should rise when the AC kicks in to about 1000 rpm to compensate for the load of the compressor. Also check if the cooling fans engage when the AC is on, they should.

[Ron Mummert]

Not that this will be of any true help, but 2 weeks ago I had a local mechanic do the R12/R132a conversion, as the '92s good old R12 system finally quit putting out cold air after 23 years of flawless service. All other system components were operating properly. I experienced no changes in drivability, & the A/C is now SO-O-O-O cold, I have to kick the temp to 75 so's not to freeze my knuckles. So....yes, something's not right with yours. Best 'o luck in tracking down the problems.

Ron.

[SVX_MY_BABY]

Originally Posted by Blacky

The rpm should rise when the AC kicks in to about 1000 rpm to compensate for the load of the compressor. Also check if the cooling fans engage when the AC is on, they should.

The cooling fans definitely come on.

But the rpm doesn't rise. It does quickly return to 700 -750 after the compressor cuts in but only after the near stumble.

Ron thanks. Mine worked great after my conversion as well. You'd never be able to tell the a/c was cycling.

[Tapani]

The svx compressor is of variable displacement type and should not cycle at all under normal conditions.

Dis you overfill the system?

I think you should only fill app 80% if converting an old R12 system to R134a.

I have used only 500g both times.

T

[SVX_MY_BABY]

Added 1.87 lb. (850g) R-134a as per retrofit sticker on car and directions linked above. Added 200 cc PAG 100 oil.

[Tapani]

Ok. I would try with less juice... But the 80% is only a general rule of thumb.

The pressure switch will cut the compressor if the pressure is too high.

T

[SVX_MY_BABY]

T
Would that cause the heavy drag when the compressor cuts in?

[SVX_MY_BABY]

I've been reading the 139 page SVX service manual section 4-7, and it states min. refrigerant 1.3 lb max. 1.5 lbs. which matches what Tipani said.

I have been working on the assumption Low side pressure should be 30 psi and high side between 185 - 215 psi per another thread I found.

All I can find in the manual is a ref to keep the low side below 40psi during charging and that the high side should be above 100 psi.

Can anyone confirm the pressures?

[SVX_MY_BABY]

[SVX_MY_BABY]

Well, the garage I'm working with has evacuated and recharged my system 3 times with their fancy machine. Still not having much success.

1st time the tech did a calculation based on the R12 sticker and charged with 1.6 lbs R134a. System would begin to cool for a brief moment the cut out each time. He suggested cleaning the condenser and area with a low pressure washer to ensure the fins were clear and air could flow. Did that, no change.

2nd time found the retrofit instructions in earlier post and charged to 1.87 lbs. No go as described above.

3rd time downloaded the 139 page service manual, printed off the spec sheet above and the relevant pages on charging procedure including the 1.3 min - 1.5 max capacity range for refrigerant and the stated capacity of 1.43 lb per the spec sheet and the instruction to keep the low side below 40 psi and high side above 100 psi while charging.

The tech tried to regulate the pressure by controlling the flow manually with the valves attached to the ports on the car. The machine aborted after 10 min. so he had to evacuate and start again. This time he set the machine to 1.43 lbs which is right in the middle of the range and per spec. Set the machine to charge via both ports.

After the charge temp read 5 Celsius (41F) in the air ducts. The compressor acted normally.

Today, overcast and 16 C outside I can't get the a/c to cool the cabin as well as using econo or vent. The line going to the condenser is ambient temperature. The line coming out is hot to the touch. The line going into and out of the drier are ambient temperature.

I'm going to try one more time. Any more thoughts?

[SVX_MY_BABY]

Not sure if it's relevant but the air temp. was 11 - 15 C on the days the system was charged.

[Tapani]

Originally Posted by SVX_MY_BABY

Any more thoughts?

Try 500g (1.1 lbs). I've done this twice..... just stop at 500g, let the system run with the machine hooked up and see how it works. You can always add more if not satisfactory.

If this does not help you may have a plugged expansion valve or receiver/drier.

/T

[SVX_MY_BABY]

Tapani, et al
I haven't done anything yet with my a/c as I've been waiting for warm weather which is finally here.
Took the car to the shop where I had it charged to see if they could do as you suggested. Do a charge to a point then stop and add a bit more if necessary. They say they can not do that. Have to evacuate and charge as set each time. The mechanic didn't mind trying again but the shop boss said three tries was enough, if they continued by just guessing they would probably take out the compressor, drier, condenser or a combination of them.

So, I found a collision shop that has a/c equipment which sits idle most of the time and for a nominal fee they will evacuate an charge a couple of times to see if it works at the lower level you suggest.

I ran the diagnostics on the a/c control unit which displayed 00 ie no codes.

Question 1. 1.1 lbs seems low for a 500g equivalent. Are you sure? and at what ambient temp.?

Question 2. A Couple of days ago the a/c kicked in and worked great for about 20 minutes then went back to kind of working. It does consistently cool a bit. Enough to make it tolerable with the windows up, but never enough to get the temp low enough to get the air circulator fan off of high. The doors appear to be working fine.
Would this point to the charge being on the edge? Just a tad high?