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I have done a lot of work on the car over the last year or so to get it back on the road, and now have got to the point where I am rebuilding the air con system. I have had the compressor rebuilt, and replaced all those air con parts that need replacing on an old system.
Before I take the car to a garage to test and (hopefully) fill the system, I wanted to see if the compressor would kick into life if I (briefly) pressed the air con button on the dash. When I tried this today, there was no sign of life on the compressor – the engine is turning the belt fine, but it didn’t look like the clutch was engaged.
This could obviously be due to some fault in the electrics, but I did wonder if the system is actually behaving how it should, given that the system is empty: I know there is a pressure sensor, and I am guessing it’s normal purpose is to stop the compressor if the pressure is getting too high, but maybe it also suppresses the compressor if the pressure is too low – or is that not the case. If not, is there something obvious i should investigate?
Run the compressor with no gas in it and the compressor will self destruct in no time due to a complete lack of lubrication.
The signal from the HVAC control unit to energise the clutch solenoid for the compressor runs through the low pressure switch and the icing switch- if either are in fault condition the compressor will not start.
The low pressure switch kicks in at about 20 psig or so.
Correct in what Fred mentioned. Add to that the AC head relay that is usually bad by now in these 30+ year old cars.
With the car not running, put the key into full accessories position. Press the AC button. If you don’t hear the compressor click, then either the low pressure switch Fred mentioned, or the AC head relay or both are bad.
I didn’t see if you mentioned replacing all the AC orings.
If the system has been down a while, did you flush the components individually? There is a great deal of old ugly mineral snot-oil settled in the low area of the components.
On that AC head relay. There are excellent threads on desoldering and replacing the relay. It’s an epiphany to hold that original little relay in your hand. Can if possibly weigh more than a few grams? Recommended replacements are far more substantial.
it’s a lot of work to revivify old AC systems. But like everything else, taking the shorter route adds time consuming detours.
my apologies if you’ve already considered all this
I appreciate your reply.
I have replaced the o rings (and some of the various ac parts) but that is about it, so i might be about to learn the hard way what i could learn from others. I haven't flushed the components i have retained.
Have rear AC? The rear AC components expelled the most ugly slime when flushed (the rear evap and the rear evap refrig lines under the car). Your condenser is the other low point. It’s not that much more trouble to flush, blow the lines out and redo. If things go boink after it’s charged, doing this redo will have seemed simple by comparison.
Not to hijack thread, but the AC hasn't functioned on my 86.5 since I got the car in 2005. Now I would like to get it functional. It appears to have been converted to 134A. What do I need to do to verify it's clean and oiled?
What type of gas was in the car the last time the acsystem ran and what gas are you planning to run upon commissioning?
If the system has not been flushed then in all probaability it should be and this is a PITA type of task!
Further more after flushing the recommended practice is to change out all the seals- whether that is strictly necesssary remains to be seen but it is what I did last time albeit I saw no signs whatsoever of any attrition on the O rings that must be changed to the green type if you are planning to use R134a.
Unless one has access to a continuous flushing machine of the type top notch ac shops have, the DIY approach is to break the system down into small sections. The ac compressor has to be disconnected, and I used an old expansion valve drilled out to permit through flow of flush media. The rear ac system does indeed complicate this process somewhat - I blanked off the spurs feeding the rear ac unit whilst flushing the front system. I also pulled the condenser out of the chassis- in part to inspect it thoroughly and in part to facilitate reverse flushing- this and I was retaining use of R134a not converting.
I just recommissioned my AC after 17 years not operational.
Fred is correct in that disassembly is the right process. I removed the rear evap, under carriage AC lines feeding the rear evap, disconnected the lines at the front evap, disconnected and removed the condenser. The expansion valves were all removed. All the removed components were flushed separately and off the car. Since the front evap had its lines disconnected, I was able to flush it in place.
I suggest this is not something to be in a hurry during the process.
you should have an air tank to feed the flush canister.
Saturday was our maiden drive with AC and it was a marvelous 34 degrees at the vents.
Essentials for flushing include hoses, canister, flush for that part. The hoses are for ducting spent flush to a receptacle. A suitable miniature wratchet is necessary for removing the expansion valve hex bolts
I appreciate your reply.
I have replaced the o rings (and some of the various ac parts) but that is about it, so i might be about to learn the hard way what i could learn from others. I haven't flushed the components i have retained.
Ian,
See if you can turn the compressor over by hand (not just the clutch, but the actual compressor).
Then, without the engine running, you can put power to the compressor clutch to make sure it engages, which will NOT damage your compressor.
If the clutch engages, and your compressor will turn by hand, the engine will generally turn the compressor.
This won't tell you that it will get cold, but those things are all a part of the process.
What type of gas was in the car the last time the acsystem ran and what gas are you planning to run upon commissioning?
If the system has not been flushed then in all probaability it should be and this is a PITA type of task!
Further more after flushing the recommended practice is to change out all the seals- whether that is strictly necesssary remains to be seen but it is what I did last time albeit I saw no signs whatsoever of any attrition on the O rings that must be changed to the green type if you are planning to use R134a.
Unless one has access to a continuous flushing machine of the type top notch ac shops have, the DIY approach is to break the system down into small sections. The ac compressor has to be disconnected, and I used an old expansion valve drilled out to permit through flow of flush media. The rear ac system does indeed complicate this process somewhat - I blanked off the spurs feeding the rear ac unit whilst flushing the front system. I also pulled the condenser out of the chassis- in part to inspect it thoroughly and in part to facilitate reverse flushing- this and I was retaining use of R134a not converting.
Even with a professional flushing machine, the system has to be largely disassembled.
You can't flush with the compressor, the dryer, or the expansion valves in place.
(Note that once those pieces are removed, there are not many "o-rings" left to be replaced with the R-134 style.)
The advantage of a professional machine:
1. They allow flow to occur in both directions (for more thorough cleaning) and then they can be switched to dry nitrogen to remove the flushing solvent. (At least that's what my machine does....not sure they all do.)
2. They are a whole bunch less messy!
3. Flushing solvent is not cheap....and it takes about 1 gallon to properly flush a system without a recovery machine. Being able to filter and recover the solvent is a big money saver.
4. They save about two hours per flush....because of 1 and 2.
Even with a professional flushing machine, the system has to be largely disassembled.
You can't flush with the compressor, the dryer, or the expansion valves in place.
(Note that once those pieces are removed, there are not many "o-rings" left to be replaced with the R-134 style.)
The advantage of a professional machine:
1. They allow flow to occur in both directions (for more thorough cleaning) and then they can be switched to dry nitrogen to remove the flushing solvent. (At least that's what my machine does....not sure they all do.)
2. They are a whole bunch less messy!
3. Flushing solvent is not cheap....and it takes about 1 gallon to properly flush a system without a recovery machine. Being able to filter and recover the solvent is a big money saver.
4. They save about two hours per flush....because of 1 and 2.
I only know of the existence of these devices but not of how the professional shops use them.
For DIY'ers having a first time crack at this I reckon they will need more like two gallons of the somewhat expensive flushing media. It took me about 16 hours of effort to complete the flushing task after my original 10PA20C seized for no apparent reason other than some internal part grenaded. These compressors are very common globally but they are far from all the same. My local friendly ac shop built me a unit using some of the elements of my compressor mated to a good compressor core for the grand total of about US$80 equivalent.
For DIY'ers having a first time crack at this I reckon they will need more like two gallons of the somewhat expensive flushing media. It took me about 16 hours of effort to complete the flushing task after my original.
Good point; knowledge that bits and pieces are in the maze of coils would require lots of confidence building flushing. In my case, there had been a working system until leaks required it evacuated. I flushed until the fluid came out “clear”.
Good point; knowledge that bits and pieces are in the maze of coils would require lots of confidence building flushing. In my case, there had been a working system until leaks required it evacuated. I flushed until the fluid came out “clear”.
I did pretty much the same [looking for the flush to be clear]- that may explain the consumption quantity I blew.
06-12-2023, 09:22 AM
Air con before it is filled
