Engine Size: 3.0
Refrigerant Type: 134a
Ambient Temp: 90+
Pressure Low: 0
Pressure High: 190+
Country of Origin: United States
Car has been converted to 134a. AC hasnt blown cold ever for me, bought the car a couple months ago. The compressor comes on and sucks the low side all the way down to 0 or even a vacuum. High side spikes, compressor stays on. NO change in dash air temp. I can see fluid moving around through sightglass sometimes, I can add freon, nothing happens. Iv changed the expansion valve with a new one. No difference. I can turn everything on, stick my hand into the evap box, touch the evap and exp valve and nothing feels cold or even cool. Ive changed the drier already.. Im stumped.. Only thing I can guess now is that the evaportator is clogged or has a ton of separated oil in it?? Lots of oil cam out when I bled system down and oil even spilling out the evap while i was handeling it, I actually took percaution to not let it spill out. Thought about blowing it out with compressed air but decided not to. Any ideas? Its getting hot in south Missisippi and Im sweating like a whore in church.
If I were working on this, I would disassemble the entire system and flush every thig except the compressor. I would drain the compressor, add in the correct amount of oil, ( I still have r12 so I would not convert), if using r134, add 80% of the r12 charge, and see what I get. Do not try to clear the sight glass with r134. You will probably end up with 90% charge. Use a new drier, make sure the condenser fan is working.
Edited: Tue May 06, 2014 at 9:32 AM by Dougflas
+1 on tear down the whole system and flush everything. The only way to be sure you have the right amount of oil is to remove it all and start over. Also a lot of "conversions" were done just by adding some other oil and not removing the original mineral oil.
Some of the elbow-style TXVs can be installed backwards, which of course does not work. The valve will slam shut and act like it is blocked. Also check that your drier is not plumbed backwards.
You might consider a new condenser, it could be blocked. Also after many miles, performance degrades as the air side gets munched up and blocked from stones and road debris.
Edited: Tue May 06, 2014 at 10:03 AM by mk378
OEM condensor on that car is a serpentine unit.
It is most likely full of trash or sealant. They are very difficult to flush, because parallel paths allow flow when others are blocked.
If the original compressor is still on the car and able to push 200 psi, then the condensor may be ok. In my experience on a used car that old the magic in a can / used car dealer / shade tree mechanic bunch have already made a big mess of things.
Backyard conversions of R12 systems can result in failed dessicant containment. A dessicant failure will trash the system as well. When you replaced the TXV, was it clean inside? Was it original, or a recent replacement?
I would contact AMA at 602-233-0090 to check on a new condensor & receiver/dryer that is compatible with 134a.
"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.
Ok update. Put gauges back on. Added more refrigerant. Low side came up to around 30-40 high side wont get over 170. Its around 75-85 degrees out. Put in more refrigerant, low side up to 40-50 high side about the same or very little higher. This was all after removing the evap again. removing the exp valve and unbolted the post valve pipe and there is like a little plastic filter in there followed by a piston looking plunger with a small orifice in it and a hole drilled into the side, this is infront of a spring. I noticed that the replacement evaps do not have this assembly as they seem to be just straight piped in the area that this contraption exists on mine. I still got no change in air temp and the evap was not getting cold or cool. I also noticed that the low side psi would kinda slowly rise and fall 30to40 then back down to 30,,, but the compressor stayed on the entire time and did not cycle..
Item you're holding is your POA valve. DId you replace it?
what does poa stand for? What does it do? No I didn't replace it. I cleaned it and put it all back together because didn't look like anything was wrong with it, I ordered a new evaporator that I believe does not have it.. new one looks like this
Im thinking maybe my compressor is tired??
Also I would like to note that I have the paperwork from when the car was converted to 134a at a Nissan dealership. This is not believed to be a backyard r12 conversion to me.
POA stands for Pilot Operated Absolute valve. It controls the evaporator pressure. I think yours is restricted causing a blockage thus 0 psi on the low side.
Did you measure how much refrigerant you charged in? Was it close to the specified weight? You should be using close to or the same amount of R-134 as it calls for R-12. When you have some pressure but no cold air, could just be undercharged.
Basically a POA valve stays wide open until the pressure in the evaporator (inlet side of the valve) goes below 25 psi. Then the valve closes down to restrict refrigerant flow, so the evaporator pressure stays the same, but the compressor pressure drops. The result of this action is the evaporator is never able to get cold enough to form frost on the fins, which must be avoided because that blocks the air flow.
Also in a properly working POA system, the compressor never cycles off during normal operation. That is what justifies the cost of the valve and why the system is used primarily on expensive cars, no cycling means a smoother ride.
0 PSI or vacuum on the low side *typically* indicates a bad expansion valve, but the 1990 thru 1993 300ZX was equipped with what Nissan calls a Suction Throttling Valve or STV. It serves the same function and operates the same as the POA that other posters have mentioned.
Since you already replaced the TXV and you're still getting 0 PSI/vacuum, your STV is probably dead, and is NLA from Nissan.
The evaporator you show a picture of does indeed appear to not require an STV, and appears to be for the 1994-96 cars. Will it fit your 1990? Don't know. You can likely remove the "guts" of your existing STV so you can continue to use the evaporator you have if the later one doesn't fit.
Do you know if your car has any provision for freeze protection of the evaporator other than the STV? If not, you're likely going to have a problem with the evaporator icing over. If it does, then you can eliminate or gut the STV without worry.
Im no longer getting 0 psi on the low side. I stated this in a later post in this thread. Im now getting pressures of 30-50 on the low side, and only 170 max on the high side.This evap came out of my 1990 car. It was already in it. The car was retrofitted to 134a by a dealership sometime ago. I dont know if this is the original r12 evap or a newer 134a style?? Couldnt find anything on that online. So I just ordered a new one like in the picture above. I have an entire parts car that hasnt been converted to 134 yet but the compressor is the same part number to my knowledge. Im going to put that compressor on when I put in the new evap and see what happens. Im going to blow out the condensor also while the system is open.
The used evaporator that you posted a picture of is the early R-12 style. The picture of the new evaporator is the later style for R-134a. Don't know if you can put an R-134a evaporator in an R-12 car. Probably not.
Warm air out of the vents doesn't always mean you have a problem on the refrigeration side of things. It could be a bad heater valve or blend door too. Did you check to see if it was dripping water out of the drain tube? If so, the evaporator is getting cold, and the air is getting reheated somewhere under the dash.
update: I fixed it. I gutted the stv* valve, stuck the old evap back in, works like a charm..
Edited: Sun May 18, 2014 at 5:56 AM by ta2003pg
the expansion valve
Lots of cars have a simple thermal switch-- they generally cost much less than $120. You will need to figure out how to integrate it into the wiring. If you don't have to deal with electric fans or a compressor rpm detector, you could just wire the switch in series with the coil of the compressor relay.
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