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Discussion Starter #1
I copied this from an earlier post and updated it with new data, and just looking for suggestions.

Well, as Steve would say, it's June, it's that time again.

A/C was converted to R-134 in September 2013 and was blowing cold until just recently (when my car died), and when I got the car running again recently it's cooling, but not very well.

In the 2013 conversion I replaced the compressor (original, rebuilt), receiver dryer, expansion valve, 0-rings, and had two of the lower AC lines converted to R-134 lines, but not replace the longest line coming from the condenser, cleaned but DID NOT replace condenser (it's still the original 1991 R-12 serpentine flow condenser), and for my testing the heater core shutoff valve is installed and closed, and AC lever is full forward, AC in recirc, engine at IDLE, etc,.

Checked pressures and dash vent temp, which was blowing in the 60s, decided to add some R-134 ( none had been added since 2013), and added a bit too much R-134 (about 10-11 ounces). After adding the R-134, with the car in the garage and the outside air around 91 the AC was blowing in the 50s at the center vent, but the pressures weren't correct (50 low/270 high), with no high side pressure drop, and the engine fan on.

Talked to Roadtrip, knew I had probably over-serviced it, so I took the car to a local shop that said they would draw the R-134 out and put exactly 36 ounces back in (for $40), but when I got the car back, it was blowing warmer than before (I suspect they just drained some R-134, since they had called me and asked what the pressures should be).

On 06/30/2015 when I checked the pressures with 92F in the garage they were 102 low/102 high static, with a fan running about a foot in front of the condenser, with engine at IDLE and with the A/C on 40 low/200 high and steady, engine fan on, 58F degree air at the center vent, with no cycling of high side pressure.

I turned the A/C off for a while with the engine still running, and when I turned it back on a few moments later, the pressures were 44 low/235 high, engine fan on but high side still not cycling, and 60 degree air now at the center vent. I would also note that the heads/thermostat never got to 198 degrees for normal fan kick on without the A/C on.

I still think I'm slightly low on R-134, but can't tell what amount I have in the system, and am curious about the fan being on with high side pressure of only 200 psi, and high side pressure not not rising to around 220, and then after turning AC off and the high side pressure getting to 235 psi, the high side not cycling down to 160 psi.

UPDATE: With 92F outside air temp here in Dallas on 07/02/2015, after driving the car for a while at highway speeds, I eventually got as low as 52F air at the center dash vent on my meat thermometer, and cooler inside the vent with laser temp gun. I have seen as low as the 40s before this problem, although that was in September, and I believe the higher the OAT here in Dallas in July may be part of the problem (A/C can only drop temp by 30-40 degrees, I think).

So could I be few (2-3 ounces) low on R-134, or just be thankful for what I hve and don't touch it?

Any ideas on why the fan isn't pressure cycling, and if I'm getting this cooling, it seems the system is working, maybe not at peak cooling, but is that possible if the whole system isn't working properly?
 

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Radiator fan will not cycle off unless freon high side pressure drops back below about 150-155 usually.

Did you notice if air recir door will close on evaporator box by passenger side wiper blade when you push recir button on a/c panel?

You might be a few oz low on freon if you can't get low side down closer to 35.

With 92F ambient system takes some doing to get dash temp much below 50.

Since you don't know what the a/c shop really did and if they have to ask you how much freon to put in system they may not be the place to service your car.
 

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Don't forget to account for humidity that will cause the A/C to not produce as cold air. 57% Humidity is pretty good amount to reduce performance.
I'd say your low as well. From Memory it's 42 oz.
 

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But Mad North-Northwest
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I suspect you just haven't gotten the charge correct. With R-134A, a bit too much performs worse than a bit too little. Usually charge by weight is 80-90% what it would be for R-12.

Here is the table I use to charge the Spider and Milano by pressure. Usually I fill to the low end of the pressure range on the low pressure gauge. Note that temperatures here are ambient air temperature.

Two tricks I've learned that help. First, do the fill in the morning on a cold engine so the air and engine are relatively cool: you get more realistic pressures that way. Second, I jumper the condenser fan switch so it runs constantly during the charge. This keeps the system in steady-state so you're not chasing the needle as the fan cycles on and off.
 

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The fan not coming on when the high side pressure is above 217.5 psi could be caused by:

1. Fan not working at all
2. Low speed fan relay inop
3. Low speed resistor inop
4. Bad brown wire from Trinary Switch to low speed fan relay
5. Bad chassis ground being provided to the Trinary Switch (black wire)
6. Bad Trinary switch itself.

The fan situation needs to be sorted out before anything else. My guess is that the low speed fan circuit is not working.

If that's not working correctly, you're chasing your tail with everything else. The following instructions presumes that the fan, it's relays, and the low speed resistor are working correctly. Are you sure you're getting a low speed fan and not just a high speed fan actuated by coolant temperature?

To check for sure, remove the low speed fan relay and jumper terminals 87 & 30 to complete the ground circuit through the low speed fan resistor. If you get nothing, then most likely the fan resistor is inop. Consequently, the trinary switch could trip on and energize the low speed fan relay and close it's contacts, but nothing is getting through the resistor, so fan motor never gets a ground.

When the hi-side A/C pressure reads 217.5 psi or higher, the fan-actuation side of the Trinary Switch should trip on (thus providing a ground for the low speed fan relay). As the hi-side pressure decreases, which it should, to 159.5 psi, at that point the Trinary Switch will trip off (cutoff the ground) the low speed fan relay and the fan stops (assuming the radiator coolant isn't tripping the fan on).

Assuming that the low speed fan circuit is operating correctly, my recommendation is:

1. Check that the brown wire to the low speed fan relay (terminal 85) is getting grounded when the hi-side pressure is above 217.5 psi.

I'd check it with the engine cold (thus preventing confusion from the radiator switch providing the ground). You can check it warm, but should disconnect the radiator fan switch to prevent confusion.

If you get no ground, start chasing the wire back to the trinary switch itself. There are two connectors (2 wires each) to the trinary switch. Choose the one that has the black and brown wire. Check that the black wire to the chassis has is permanently grounded. If not, that's most likely the problem. The trinary switch could be working, but if the chassis wire isn't providing a ground, then the switch can't do it's job.

If black chassis wire IS providing a permanent ground, then run the A/C with the brown/black wire connector disconnected from the trinary switch. When the pressure reaches 217.5 psi, check with an ohm meter or test light that the switch closes and the brown wire grounds. If it does, then check the continuity of the brown wire between the trinary switch and the low speed fan relay.

In short, what we're trying to do is check that the ground from the chassis makes it through the trinary switch and to the low speed fan relay.

If the low speed fan circuit is indeed roached, then you can connect the brown wire from the trinary switch to the high speed fan relay terminal 85 (brown-white wire from the radiator thermal switch). I'd also disconnect the brown wire from the low speed fan resistor just to take it out of play until you can get a new one.
 

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But Mad North-Northwest
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I thought he said the fan was coming on, just not turning off? Or did I misunderstand?
 

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No, you're probably right, but my concern was making sure the fan is cycling on/off by command of the trinary switch and not the radiator switch confusing the issue.

I had a little trouble following the narrative, Curt sometimes writing a bit in Faulknarian style. I'm allowed to use that word. I was an English major.
 

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Discussion Starter #8
Thanks all and Happy Fourth of July.

Sorry, thought I included all the facts, but I missed including that the re-circulation door does in fact close, the AC lever is full forward, and the fan is on when the A/C is on.

It is hot here in Texas, temperature in the low 90s with humidity in the 50s, so it's a tough combo to cool.

I had the shop, who I use off and on and do good work for a great price, to evacuate the R-134 and put exactly 36 ounces of R-134 back in, which is supposedly the amount of R-134 recommended on here after conversion from R-12. The shop asked for the pressures because they had no pressure values for a 164L conversion, even though the mechanic knew from his computer that there was an R-12 placard in the engine compartment.

Suspect that the system is low by 2-4 ounces of R-134, maybe 38-40 ounces, or 44 ounces as Jason suggests, of R-134 is a better number than 36 ounces, but with 36 ounces of R-134 I'm getting fair cooling, 52 degrees at center vent this morning, with a black leather interior and huper-optik tint.

I write the post the way I do because I re-write trying to anticipate all the questions to be asked to enable analysis of the problem without having to play 20 questions, but the writing professor at Command and Staff said I write well for an Aggie/engineer/Marine, but in the style of Thomas Pynchon, not Faulkner, whoever he was.
 

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No clue. Had to look him up . . . . Pynchon, "noted for his dense and complex novels."

Faulkner was noted for his signature "stream of consciousness" style.

Will cogitate more on the A/C quandry.
 

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But Mad North-Northwest
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At least on the Milano, the AC outlet temperature is supposed to cycle between 45F and 54F via the thermistor. Not sure what the spec is on the 164 but if it's similar to the Milano you're not too far off.

In any case, follow my advice above and measure the low side pressure vs the table. That'll give you some clue if you really have too little (or too much) refrigerant. Don't just add more or you're quite possibly going to be in the same boat you were before: again, 134A cools better on the low side of charge vs. overcharged.
 

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Discussion Starter #11
Thanks for the advice and the chart, Gubi.

I'm not sure how similar the 164 A/C system is to the Milano's system, (with the 164 high pressure building up to app 218 psi, and then dropping down to around 165 psi as the fan kicks on, then building up and cycling down, etc.) but I do think I'm still low.

And being a good citizen who cares about the environment, it would really be nice if they sold R-134 in 4 ounce cans, so you had less to waste.
 
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