My diagnostics have shown a code 51. After reading a bunch of threads I found posted I checked the throttle position sensor and it checks out. So the A/C problem isn't just my imagination. The system was recently charged with freon and it doesn't leak. The compressor seems to work. The A/C does cool some but has not been cooling as well as I expect all the time. More often than not the interior temperature has been just a little better than outside temp, maybe 5 to 10 degrees cooler with temp setting on lowest and fan on high. Any ideas on how to approach testing and finding the problem would be appreciated.
Any good advice on A/C testing? 87 7mge
- Thread starter Dave C
- Start date
Do you have the values for what you system is running ie what is the high and low pressures when at idle and when at 3000 free rev with ac on. You want around 30-50 on the low side and 230-270 on the high side this will vary with engine rev. At idle ur looking on the high end of the low side so 50 and low end of high side so 230, then at 300 ur looking more around 30 on low and 270+ on high. These numbers will vary with altitude, humidity and temperature outside.
As for diagnostics if you high side is too high then its probably something condenser related so check your ac fan and normal fan and check for blockage of airflow through condenser. Next if you high side is low and low side is high your most likely looking at a compressor issue, or a low charge. If you high side is low and low side is low, most likely low charge or could be a restriction or could be a thermal expansion valve problem. And if you high side is high and low side is low, look for a blockage in the liquid line, probably at the orifice tube. And thats about the cut and dry of it there could be other problems but these are the most common. And one last thing make sure the compressor clutch comes on and stays on, if it only comes on for a second then you could have a bad low pressure sensor or a low charge, if pressures on low side are above 25 and the compressor is cycling off then check sensor and check clutch coil.
And the code 51 could be a lot of things like ac is on when you start the car or your pressing the peddle when u start it or other things.
As for diagnostics if you high side is too high then its probably something condenser related so check your ac fan and normal fan and check for blockage of airflow through condenser. Next if you high side is low and low side is high your most likely looking at a compressor issue, or a low charge. If you high side is low and low side is low, most likely low charge or could be a restriction or could be a thermal expansion valve problem. And if you high side is high and low side is low, look for a blockage in the liquid line, probably at the orifice tube. And thats about the cut and dry of it there could be other problems but these are the most common. And one last thing make sure the compressor clutch comes on and stays on, if it only comes on for a second then you could have a bad low pressure sensor or a low charge, if pressures on low side are above 25 and the compressor is cycling off then check sensor and check clutch coil.
And the code 51 could be a lot of things like ac is on when you start the car or your pressing the peddle when u start it or other things.
Meh, just measure the temp of the suction line where it exits the firewall. That way you'll know if it's refrigeration or a ducting/damper issue. Like meta I'm betting on a refrigeration problem though...
Is the system still R12? was it ever left "open" in the past?
I had several MKIIIs which were not as cold when converted to R134. I do not think that it's the refrigerant, but the inefficiencies of the system. After being left open for awhile, things get oxidized and the dryer/receiver is already wore out, the condensor has clogged up a bit w/any debri left in the system and the design makes it almost impossible to thoroughly clean.
In the latest conversion, I used the A/C refill info from the tech section of the forum (tells you how to use the guages, vacuum the system, etc), but also replaced the condensor with a parallel flow (newer design) one. Look for my write-up for the numbers/results. Very happy with it.
Good luck. I hope you find/resolve your A/C issue.
I had several MKIIIs which were not as cold when converted to R134. I do not think that it's the refrigerant, but the inefficiencies of the system. After being left open for awhile, things get oxidized and the dryer/receiver is already wore out, the condensor has clogged up a bit w/any debri left in the system and the design makes it almost impossible to thoroughly clean.
In the latest conversion, I used the A/C refill info from the tech section of the forum (tells you how to use the guages, vacuum the system, etc), but also replaced the condensor with a parallel flow (newer design) one. Look for my write-up for the numbers/results. Very happy with it.
Good luck. I hope you find/resolve your A/C issue.
Dave C;1602239 said:
Uh, I meant where it exits the firewall into the engine bay. Maybe you should just take it back to the shop that charged it...
^ Hehe agreed, back to the shop. But as jetjock said the suction line is the line coming out of the firewall going back to compressor. It should be cold and covered in water when ac is running. If it is not then you need to find out what is wrong with the system, if its cold then its a blend door problem or a controller problem. As for it not getting any colder when on 86 or 60 it wont, if its not as cool in the car as the setting is it will just run at full, ac it either on or off there is really no in between, the blend door and fan speed are what give you cooling from there. If the temp you want is 75 and the interior temp is 78 the auto control will turn down the fan speed some and when you get to the desired temp it will keep it there by either modifying the blend door pos or the blower speed or shut the ac off until needed again.
Main things to check, 1 compressor clutch is spinning when car is running and ac is on this should be a constant spinning, 2 ac discharge line (the larger of the two coming out of the fire wall) is cold to the touch.
Main things to check, 1 compressor clutch is spinning when car is running and ac is on this should be a constant spinning, 2 ac discharge line (the larger of the two coming out of the fire wall) is cold to the touch.
So, you figured out I am not a formally trained mechanic...well done. LOL
It is still R-12 and I can't vouch for what all was done to the car before I bought it. I know it went without refrigerant in it for at least 3 years though.
I ran the A/C for 10 mins or so, then the suction line was not cold to touch or wet but definitely cooler than other parts around there... Maybe same as outside air temp. Read about testing the magnetic clutch in TSRM but this will be a first other than listening to it. I could use a clearer explanation if youve got one. "Take it to the shop" sounds too easy and expensive though at the moment.
I think it is cooling well for seconds at a time. Thanks you three for your ideas and input.
It is still R-12 and I can't vouch for what all was done to the car before I bought it. I know it went without refrigerant in it for at least 3 years though.
I ran the A/C for 10 mins or so, then the suction line was not cold to touch or wet but definitely cooler than other parts around there... Maybe same as outside air temp. Read about testing the magnetic clutch in TSRM but this will be a first other than listening to it. I could use a clearer explanation if youve got one. "Take it to the shop" sounds too easy and expensive though at the moment.
I think it is cooling well for seconds at a time. Thanks you three for your ideas and input.
Three years without refrigerant is bad news. Even if the system worked now I wouldn't expect it to last long unless the shop went above and beyond the call of duty.
Anyway, look at the front of the compressor where the clutch is. The part at the very front which has the belt on it spins whenever the engine is running. The part directly behind couples to the front part and spins when the AC in on. If it's not the clutch isn't energizing. Alternately you can watch it with the engine off. You should see it move slightly and hear it click when the AC is turned on because there's nothing in the system that requires the engine to be running in order to activate the clutch.
If the clutch is working there's little else you can do. Although I'm a big fan of DIY some things require specialized tools and knowledge. This is one of them. It also bring to mind an old axiom: "If you think having a professional work on something is expensive, wait until you have an amateur do it"...
Anyway, look at the front of the compressor where the clutch is. The part at the very front which has the belt on it spins whenever the engine is running. The part directly behind couples to the front part and spins when the AC in on. If it's not the clutch isn't energizing. Alternately you can watch it with the engine off. You should see it move slightly and hear it click when the AC is turned on because there's nothing in the system that requires the engine to be running in order to activate the clutch.
If the clutch is working there's little else you can do. Although I'm a big fan of DIY some things require specialized tools and knowledge. This is one of them. It also bring to mind an old axiom: "If you think having a professional work on something is expensive, wait until you have an amateur do it"...