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So there's a few things on the AC. We've been texting back and forth on this.
First there's the PowerFC AC problem. Many times the AC will just blow cold on speed 1 and 2, but speeds 3 and 4 it's intermittent or not at all. If you look at the sensor check screen you can watch the AC light on the screen, if it just flat won't come on with speed 3 or 4 (or is intermittent) you will need to add a relay to sort that out. There's a few write-ups on it. I need to do this on my car.
Second is it's hard to get a proper R134a charge sometimes. It's easy to over-charge it, which puts more load on the compressor. If you are driving at constant speed on level ground do you "feel" the load of the AC compressor kicking on and off? Like the engine bogs a little bit? It's not supposed to do that. An FD from the factory had no discernible difference in driveability with the AC on. Again, a lot of this problem is the 134a conversion, our system doesn't run it very efficiently.
Speaking from from A/C experience here lately, I'd recommend checking a number of things:
1) Your TPS for idle issues and making sure your PFC was able to learn idle when it was installed.
2) As for your car suffering under load, take the car to get the r134a evacuated and do a vacuum test.
3) If your vacuum test is all good, you may need to try adding the r134a into the system a little at a time and watching the pressures. I found that mine needed more than the recommended r134a but not by too much. There was a sweet spot and now the system doesn't have any issues and blows super cold even in 95 degree ambient temp at idle.
That being said, make sure whatever A/C shop you take it to will let you help them... and work with you to get it right. Luckily, the shop I had across the street let me do the work with the tech on the car.
So there's a few things on the AC. We've been texting back and forth on this.
First there's the PowerFC AC problem. Many times the AC will just blow cold on speed 1 and 2, but speeds 3 and 4 it's intermittent or not at all. If you look at the sensor check screen you can watch the AC light on the screen, if it just flat won't come on with speed 3 or 4 (or is intermittent) you will need to add a relay to sort that out. There's a few write-ups on it. I need to do this on my car.
Second is it's hard to get a proper R134a charge sometimes. It's easy to over-charge it, which puts more load on the compressor. If you are driving at constant speed on level ground do you "feel" the load of the AC compressor kicking on and off? Like the engine bogs a little bit? It's not supposed to do that. An FD from the factory had no discernible difference in driveability with the AC on. Again, a lot of this problem is the 134a conversion, our system doesn't run it very efficiently.
Dale
Since we've been texting, I'll rehash what I did so the wide audience can chime in with ideas/suggestions.
I did the PFC Idle Re-learn procedure and that definitely helped with my idle issues. The only challenge I seem to experience now is that my if I'm half to wide open throttle and let off the gas in neutral, the car stalls or comes very close to stalling when AC is on. If I come to a more gradual slow down to neutral, no issues. I think what's happening is that the throttle is closing too fast and the car is stalling. I pulled my dashpot and it's functional. I have about 1/4 inch of white showing. It's hard to push down and quick to rebound (which FSM says is the intended behavior). I also sprayed some carb cleaner on it to clean out any crud. I have it adjusted as far as it will go. If I had another 1/8 or 1/6" of room, I think it would stop the throttle but it's threaded in as far as it will go and It barely dampens. See video and picture. I might see if I can find a thinner lock nut because that would give me some extra space for sure.
I'm going to mess with my FC IDLE settings in the PFC and see if raising them helps. Right now, FC A/C is set to 1300 rpm so I'm going to try and raise it. I'll test drive it and see what load AC puts on the engine while driving on level ground. I already did the PFC Relay fix and it is definitely intermittent on fan speed 3 and 4 but fine on 1 and 2. I previously had AC running before this whole VMount project and it worked fine on all 4 speeds but my relay does click properly when I push the AC button still. I'm going to have to pull the **** and see if the contacts need cleaning off. My fear of course is removing the trim panel and something breaking. I have no idea how much R134a was put in, but I assume the fancy pants SnapOn AC machine the shop had was smart enough to know based on outside temp and the low side pressure?
Speaking from from A/C experience here lately, I'd recommend checking a number of things:
1) Your TPS for idle issues and making sure your PFC was able to learn idle when it was installed.
2) As for your car suffering under load, take the car to get the r134a evacuated and do a vacuum test.
3) If your vacuum test is all good, you may need to try adding the r134a into the system a little at a time and watching the pressures. I found that mine needed more than the recommended r134a but not by too much. There was a sweet spot and now the system doesn't have any issues and blows super cold even in 95 degree ambient temp at idle.
That being said, make sure whatever A/C shop you take it to will let you help them... and work with you to get it right. Luckily, the shop I had across the street let me do the work with the tech on the car.
1. TPS is good. Car idles perfectly with no AC. I reset the PFC and had it re-learn the idle. It didn't surge at all so that makes me wonder if it learned anything but I did a full factory reset, reloaded my map, and then did the idle learn procedure as instructed in @DaleClark 's PFC FAQ
2. The shop that filled it pulled a vacuum and it did not see any leaks
3. I need to get a gauge and see what the pressure is. The challenge is I don't know what the PSI should be based on the temp. I'll have to check google to see if there is a chart. Are you running R134 and what is super cold? I do have the Rx8 condenser on mine but I dont think a problem at all.
I might be wrong, but the intermittent signal could mess with your idle if the ECU is rapidly switching to and from AC idle as the signal comes and goes. Weird that you are still getting a dirty signal even with the relay mod.
It sounds like the contacts in your fan speed switch could have some corrosion. It's not too hard to get the switch out and clean it off.
Are you on the default PFC tune? One thing I did notice after running my tune through FCTweak is that all my stalling out and idle issues vanished completely (at least so far). Obviously rule out all the potential analogue causes first (bleed screw, throttle stop, dashpot, TPS, etc) but it sounds like you have already taken a look at most of those.
I might be wrong, but the intermittent signal could mess with your idle if the ECU is rapidly switching to and from AC idle as the signal comes and goes. Weird that you are still getting a dirty signal even with the relay mod.
It sounds like the contacts in your fan speed switch could have some corrosion. It's not too hard to get the switch out and clean it off.
Are you on the default PFC tune? One thing I did notice after running my tune through FCTweak is that all my stalling out and idle issues vanished completely (at least so far). Obviously rule out all the potential analogue causes first (bleed screw, throttle stop, dashpot, TPS, etc) but it sounds like you have already taken a look at most of those.
Not running default tune. Just got my car back from a dyno on Friday (Scroll back a few posts). My AC was not working when on the dyno (it was diagnosed after the dyno tune), but aside from the half to WOT off throttle stall with AC on, the car otherwise idles fantastic. My tuner runs all his tune through FCTweak.
Ah fair enough. Sorry if you mentioned that above. That was just the magic thing that seemed to clear my issues up after knocking my head on them for a long time.
So fan speed 2 at idle, does the AC seem to work/cool properly? Does it still cut in and out when you get on the gas on one of those fan speeds? Or at this point is the idle stall really the main head scratcher?
I am not sure how much the RX8 condenser impacts the overall system capacity, but I can see where that might have thrown their fill-up off if they just filled by weight based on the capacity listed on the hood sticker. Harbor Freight has a decent gauge manifold set they sell that isn't crazy expensive or anything. The pressure readings can tell you a lot if you can reproduce the problem at idle.
1. TPS is good. Car idles perfectly with no AC. I reset the PFC and had it re-learn the idle. It didn't surge at all so that makes me wonder if it learned anything but I did a full factory reset, reloaded my map, and then did the idle learn procedure as instructed in @DaleClark 's PFC FAQ
2. The shop that filled it pulled a vacuum and it did not see any leaks
3. I need to get a gauge and see what the pressure is. The challenge is I don't know what the PSI should be based on the temp. I'll have to check google to see if there is a chart. Are you running R134 and what is super cold? I do have the Rx8 condenser on mine but I dont think a problem at all.
I'm running R134a. The car was converted over in Japan. Low pressure should be between 25-40psi for correct cooling.
By super cold... well I guess it is all subjective (since I haven't put a temp probe in), but to me it feels like I'm in a freezer hanging meat. Usually converted cars do not get as cold as their R12 counterparts, but I think if you hit the sweet spot on the fill, you'll notice a difference. My car has factory everything right now minus the catback.
Also... the car stalling on lift off is almost always the throttle settings. Since the car uses a mechanical throttle body it is your ECU setting most likely/sensor that is causing the car not to catch the plate closing and returning to idle. I had this problem on one of my old FDs where on lift off the tach would miss returning to the 800prm idle on a decel with the a/c on and try to stall out. IIRC, what I did was adjust the throttle screw and adjusted my A/C rpms up on the PFC.
Last edited by twinturborx7pete; 07-13-20 at 07:19 PM.
Good News: I raised the FC A/C idle setting in the PFC from 1100 to 1380 rpm and the car no longer stalls in neutral with the AC on!
Bad New: The compressor still intermittently cuts on and off. When I first got in the car and drove the AC was on for a good 10-15 minutes. Zero stalling. After that, I'd be cruising and look at the PFC sensor check and see the AC light go out. It would stay out for 5-10 second and then come back on. This was not under heavy load at all. Sometimes it would not come back on, other times it would not. @DaleClark I could not feel any difference or bogging down of the engine when I turned the AC on or off.
I used the cheapo gauge that came with the R134 refill can (which I really don't trust if you read my older posts) since I had it on hand. With the compressor OFF, the pressure read 45psi. With the compressor ON, it read about 25psi. It's currently 74 degrees out and the gauge says that's low for this this temp but again, I don't know if I fully trust it so I take this with a grain of salt. @SpinningDorito O'Reilly Auto loans a manifold gauge set for free. I may need to grab it this weekend and see if I can reproduce the on/off compressor issue while the car is idling in my driveway to see what my high side pressure is.
My thoughts are could be a charge issue (over/under) or it could be something related to why even with a relay, my AC only comes on reliably with fan setting 1 or 2 but not 3 or 4. I do have another relay I could try but the relay I have now absolutely clicks when I press the AC button and it grounded to the same point on the chassis as my PFC so I'm pretty sure it's a solid ground since my PFC hasn't cut out me (yet). As mentioned above, I should try and clean the fan speed switch. I just gotta find a post on how to pull it and hope that if it involves trim nothing break on this fragile *** car.
I am still unclear, does your AC still cut out when you keep it on speed 1 or 2? Or do you only start to get warm air out the vents on speeds 3 and 4?
Hard to say anything on the pressures without the high side reading as well. 25 psi at idle does seem kinda of low to me though (but I don't use 134a so I could be wrong)
Fan switch is fairly easy. Pull the *** off, and loosen the little nut with some needle nose pliers (it shouldn't be on there super tight), make sure not to drop/lose the nut/washer once they are loose.
After that, just pop the radio out and you can reach up and pull it out, there is one electrical connector you will need to disconnect from the pigtail on the back of it.
I am still unclear, does your AC still cut out when you keep it on speed 1 or 2? Or do you only start to get warm air out the vents on speeds 3 and 4?
Yes. AC will cut out randomly on setting 1 or 2. It was 75 out tonight so even when it cut out the air was still relatively cool. It will be hotter than hell tomorrow so I can test again if I have time when it's hot, but according to the PFC, the AC definitely cut out since the indicator showed it was off. I'm going get some gauges this weekend and then follow this https://rechargeac.com/how-to/ac-system-pressure-chart to at least try and narrow down. Could be pressure related and the pressure switch is just cutting off or it could be relay/fan contact related or it could be something like my expansion valve needs replacing
That's interesting. I didn't think the low pressure switch would cause the PFC light to turn off, but that's just foggy memories from the last time my AC system was at atmosphere (no pressure/gas). I thought that light was simply the input the ECU gets from the AC and fan speed circuit.
If the light on the commander is always showing off when it cuts out (even on 1 and 2 speed) then it sure seems like some sort of electrical issue, unless I am just completely misremembering what I said above.
That's interesting. I didn't think the low pressure switch would cause the PFC light to turn off, but that's just foggy memories from the last time my AC system was at atmosphere (no pressure/gas). I thought that light was simply the input the ECU gets from the AC and fan speed circuit.
If the light on the commander is always showing off when it cuts out (even on 1 and 2 speed) then it sure seems like some sort of electrical issue, unless I am just completely misremembering what I said above.
I’m leaning toward electrical as well, but i know if the pressure switch is too low, the compressor cuts off so I guess the question is if the pressure switch cuts off the compressor, does it let the PFC know, hence the light going off?
Regardless of what the gauge says, the system does blow cold air so if the pressure was so low that the AC pressure switch kicked off, would I even get cold air?
I wouldn't bet my life on it, but from what I remember the low pressure switch does not change the PFC indicator for AC (but it will cut off the compressor if needed).
@Djseto it sounds like your charge is either under or over. I was having the same issue and it came down to my charge being off with the r134a. I'd recommend getting the entire system evacuated and starting over with refrigerant. With the machine you can add in or remove incrementally to assure a proper charge where the compressor won't surge or cut off.
It is normal with a properly set up and charged AC for the compressor to cycle on and off. Most times it's from the sensor in the evaporator core in the dash. If temperatures get too cold in the core, it cuts the compressor off for a bit, then turns it back on when it warms up. This is to prevent the core from frosting/icing over.
There's a temp probe snaked into the core that goes to a connector, that will cut the 12v to the compressor.
Again, that's totally normal. You do also have a pressure switch in the high pressure line going to the evaporator up front that can cut it off when pressure gets too high.
When the compressor is running, it's normal to see 25-40psi and the pressure will go up when the compressor is not running. You are also only seeing half of the picture since you don't have a full manifold hooked up showing low and high side pressures. Normally the low side is low pressure, high side is high when the compressor is running. When it's not running low comes up and high goes down, they eventually will equalize at the same pressure since nothing's acting on them (the compressor) to pressurize the system.
If the system is cooling OK and the car is driving OK, you're OK.
It is normal with a properly set up and charged AC for the compressor to cycle on and off. Most times it's from the sensor in the evaporator core in the dash. If temperatures get too cold in the core, it cuts the compressor off for a bit, then turns it back on when it warms up. This is to prevent the core from frosting/icing over.
There's a temp probe snaked into the core that goes to a connector, that will cut the 12v to the compressor.
Again, that's totally normal. You do also have a pressure switch in the high pressure line going to the evaporator up front that can cut it off when pressure gets too high.
When the compressor is running, it's normal to see 25-40psi and the pressure will go up when the compressor is not running. You are also only seeing half of the picture since you don't have a full manifold hooked up showing low and high side pressures. Normally the low side is low pressure, high side is high when the compressor is running. When it's not running low comes up and high goes down, they eventually will equalize at the same pressure since nothing's acting on them (the compressor) to pressurize the system.
If the system is cooling OK and the car is driving OK, you're OK.
Dale
Good to know. I'll go drive it today when it's in the 90s and see how it cycles. Since it was cooler last night, I can see it cycling more because it's not as hot out. I assume when it's really hot out, it should not cycle as much since the core probably won't have "time" to get too cold.
If you have any kind of thermometer to monitor the vent temperature in the cabin that would also help you tell if the compressor is cycling due to the temperature probe. Even a cheap food thermometer should work.
One thing to note is that higher the fan speed (or the warmer it is in the cabin), the less often it should cycle due to the evaporator core getting too cold. That seems like the opposite of what you said you are seeing above (speed 3 and 4 cutting out more often)
Just took the car out for a 10 minute drive. It's 89 outside with 63% humidity. My app says it feels like 98. The compressor def cycles on and off a lot, BUT it never got warm. It did cycle less on fan settings 3 and 4. All in all, per @DaleClark , if the car is driving OK (it is) and cooling ok (it is), then I'm OK (?). I stuck a food thermometer in the driver side door vent and it read 50 degrees and was plenty cool for me. The easiest way for me to test the 3 and 4 fan setting/relay/contact "problem" is to just put the car in ON (but not start) and hit the AC button while the fan is on 3 or 4. If it doesn't show on in the PFC, it's gotta be an electrical issue. Otherwise, maybe I'm trying to find a problem where there isn't one.
You generally want to measure from the center vents, just FYI.
50 out of the door vent sounds about right though, I'd guess that would put the center vent around 40-45.
One thing about your test is that at least on my car is that the PFC ac issue doesn't necessarily act the same way with the engine running vs just on ignition power.
On my car specifically, fan speed 3 does not kick on the AC consistently when the car is running, but looks fine on the PFC on just ignition power.
You generally want to measure from the center vents, just FYI.
50 out of the door vent sounds about right though, I'd guess that would put the center vent around 40-45.
One thing about your test is that at least on my car is that the PFC ac issue doesn't necessarily act the same way with the engine running vs just on ignition power.
On my car specifically, fan speed 3 does not kick on the AC consistently when the car is running, but looks fine on the PFC on just ignition power.
Funny enough, I measured from the center vent (drivers side) and it was probably a 2-5 degrees warmer. The coldest output was the door. I had the fan on 4 and was re-circulating the air.
So besides enjoying/driving, what's next on the agenda for the car?
Dale
I need to schedule an alignment. Aside from that, performance wise, I think the car is good . Nothing else so long as nothing breaks. At some point, I'll replace/upgrade the stereo and then just save up for body work. I need a new hood and new paint job. I've been quoted 5-7k so that might be down the road since I've blown through a few grand the past few months and I'm sure the wife would like me to slow down the bleed. I got a new R1 lip that I'm going to mount this week once I have the fasteners (had to order them from Fastenal).
Maybe next year, I might do an upgrade to a Haltech but the PFC is tried and trued so we'll see...
Another AC update, a mystery to solve, and one more thing to fix...
I finally bit the bullet and got some AC manifold gauges since I got tired of driving back and forth to O'Reilly Auto to borrow them. Up until today, I had been all over the internet looking for temp/PSI charts for R134 like this one but then I'd stumble upon other sites via Google that have conflicting info to other sites. When I was following the chart in the link, I could not get the high side pressure to be 250-270 and the low side to be 45-55psi no matter how much I added or removed. This led me to believe I had either a compressor problem or an expansion valve problem. It turns out I was kinda chasing a non-existent problem. It occurred to me after googling sites and reading time after time that R12 went away around 1993 that perhaps the 94+ FDs used R134.
I went and found the 1994 FSM (specifically Body/Electric Troubleshooting Guide) and sure enough, it has the proper operating specs and troubleshooting procedure for R12 AND R134. I swear this should have been obvious but I haven't come across any threads regarding R12 to R134 conversion that mention just looking at the 94 FSM. According to the FSM, the only differences in the system are the O-Ring types, Compressor Oil, and charging valves. The rest appear to be the same (Section G-4). The FSM says that for R134 systems with 86-95 degree blower inlet temps, the low side pressure should be 22-35psi and the high side should be 199-228psi. This was VASTLY different from the temperature charts I found on the web for R134. No wonder I could never quite get it working on my own following those guides OR the stupid cheap low side gauge that comes on those recharge cans. BTW, the cheap gauge I was previously using was 10psi off from the manifold gauges.
Now that I had that sorted, I still couldn't quite get my pressure readings right. I kept getting about 40psi low and 160psi high when compressor was on. Then I saw in the FSM that to test pressure, it says to have the car idle at 1500RPM for R134 (2000rpm for R12). This leads me to what might be a "problem": I adjusted my IDLE A/C settings in the PFC and no matter what value I set, the idle stayed at 950-1000rpm. This makes me think my PFC isn't able to control the idle because when I adjusted all the other IDLE settings, the idle never went up. The car itself idles good, but I don't think it works. Maybe @DaleClark or another PFC guru can chime in. I know the Fuel Cut works because setting it higher is what stopped my car from stalling when I lift off the gas in neutral.
Anyways, I was able to look at my PFC through the windshield and manually open the throttle and do my best to hold it at 1500rpm and sure as ****, the needles began to move and settled in at 30psi low and 200psi high on this hot 90 degree day -- right in spec! I hopped in the car and the air was "cold" at idle (1000rpm) but when I started to give it gas and hold it at 1500+rpm while sitting in my car, the air got colder. I didn't bother to pull a thermometer to see the actual temp because it was cold enough for me. I got in the car, took it for a ride, and enjoyed nice cold air. Sometimes in fan 3 or 4, it would cut out and blow warm air and I'd have to turn it back to 2 but for most of my drive it cycle'd on and off as needed without any loss of cool air. Still gotta hunt that down but I'm hoping pulling the **** and cleaning it off will fix it since I have the relay fix already. AC Problem (mostly) solved!
So as I'm driving and enjoying the cold and air freshly tuned ride, I look over and see my Innovate MTX-L Wideband with readings that are all over the place. They made zero sense and it was slow to respond. Another mile or so later, it throws E8 Error. According to the manual it's a bad sensor. I had read these things tend to burn out and prior to the new Turblown down pipe, the previous DP had the bung close to the turbo and I was tuned rich, so it lasting ~1500-2000 miles is probably not bad. I searched here and it appears they tend to burn out but I saw a post from @arghx that the issue is likely more with Innovate Controllers than the actual Bosch O2 sensor. Elliot at @Turblown suggested an AEM X Series Wideband which aligns with some old posts I found here as well. They use the same sensor but don't seem to have the same failure rate. I decided to order the the O2 sensor for now and if it goes bad down the road, I'll move to AEM. Even thought my car was tuned last week, I still prefer to have a working Wideband so the car is again on jacks waiting for the O2 sensor to arrive.
So...for the PFC...any thoughts on this idle thing? I know when I did the idle learn process, my car did not surge or anything. Again, my idle appears to be very solid after Rotorsports tuned it, but if my PFC is supposed to be able to adjust the idle, then something probably still needs to be addressed. Thoughts?
07-13-20, 09:19 AM
. Temps are about right for 134a. 