Ac issues

[87GrandMarq]

I’ll check tomorrow. The hood does vibrate but I don’t think that’s what caused the bouncing. As it was idling it was only getting into maybe the low 60s high 50s. Also that’s a new compressor, supposedly.

Anyway I’ll test it, take it for a spin then test again tomorrow.


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[sly]

Rule of thumb is that the high side on a 134a system that uses an orifice tube should be about 3x what the ambient temp is in Fahrenheit. So about 250-270 ballpark. The system may be a little low, but it's not far enough off to really give the issues you've been dealing with in my opinion.

[gadget73]

yeah I wouldn't say its overcharged either. If the charge is low enough that the compressor cycles off, that would do it.

Another thought, if the blend door is not fully to cold, you'll get poor AC performance. It will also show as low pressure since its not getting a full heat load. Bad foam on the door causing a poor seal, or if someone replaced the evaporator and did not put the foam back around it won't work so well. A dirty evaporator will also cause poor performance. If you pull the blower out, you can see part of it. Might be worth doing to see if its all covered in crap. No filters on these so whatever comes in through the blower goes into the heater and evaporator cores.

[87GrandMarq]

Evaporator is brand new so I doubt that’s the issue. I checked for air leaks around the evaporator, none. Blend door, all the way closed. No leaks that I can find. So I did what was suggested, I added some more refrigerant and I revved it for at least 10 seconds or so and the low side dropped to about 20 psi but the compressor didn’t cut out. It still did drop though so what does that point to? Not enough airflow across the condensor?

Also when I added refrigerant when I opened the valve it would climb 5 psi then fall back down and took forever to charge.

Today is probably a little cooler than the last time I checked but with the fan motor on high it dropped to about 56* or so, so I guess more refrigerant is needed.


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[gadget73]

The pressure differential will get higher with more RPM because the compressor is doing more work. Not too surprising really. If its a problem with airflow on the condenser usually the pressures just go up. I usually run it steady at ~1800 and mess with it from there.

Could be the charge connections are a bit crappy. The original ones with my gauge set had some internal problem where they had very restricted flow. It barely charged and it just didn't respond like it should. I've also had issues with the can taps not always giving a full puncture or depressing the valve. Newer cans use a different tap too, not sure what combo of stuff you're using. I don't exactly know what will happen if you use the older style tap with the new self-sealing cans.

[87GrandMarq]

There is an adaptor for the self sealing cans, that’s what I use along with a can tap. It works fine but can leak when screwed in/out a certain bit. Maybe the tap isn’t working right.

I’m thinking maybe at this point it’s just a little low. I’ll try charging it a bit more soon.


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[sly]

Nice thing about the older systems is that the valves are replaceable. The newer R134a systems have solid low and high side valves that you can't replace. You have to replace the entire line. If the valves are leaking, they may just need to be snugged up. You will always get a little bit of a leak when applying/removing the fittings. I do know that newer gauge sets don't have a long enough center pin to actually contact the retrofitted valves on my car and I had to rebuild my old gauges to be able to service mine.

[87GrandMarq]

Both of my fittings leak, moreso the low side so when I take the cover off you get a rush of refrigerant that leaked and was stuck under the cap. The high side stem keeps bending when using my new gauges but I attribute that to the crappy cheap quality.


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[87GrandMarq]

Another twist. Today it took a while to cool and only got down to 60* on max ac high speed fan. Pretty much the same ambient temps as yesterday. Also I noticed a lot of sweating on the lower line to the evaporator past the oriface tube, but nowhere else. After idling longer the drier started to condense but wtf why is it taking longer than before. It used to condense pretty quickly even if it didn’t cool that well. I’m about to evacuate the system and start from scratch.

It’s frustrating because it worked very well when I first set it up then went downhill after that.


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[87GrandMarq]

Ok so I did more testing. Today it took forever just to get to 60* so I added a little bit more because the low side was reading about 32 psi. I added more and it got up to about 40 psi. I figured with the high temps and humidity that was about right. Well it was still around 60*. So I took it for a spin and sure enough it got down to about 50*. Then when I got back I but the gauges back on and the low side was 30 psi again. But now the drier and low side lines were sweating profusely. Discharge temps were in the high 40s. Before I could get it to about 40* but this was a little win so I took it. As it idled the low side started creeping up and got to about 35 psi so I grabbed my pusher fan that’s been sitting and mocked it up in front of the radiator and sure enough within a minute it dropped to about 30 psi and stayed there. The discharge temp was in the upper 40s. Maybe with two pusher fans it’ll cool as well as any factory r134a system but I’m still stumped why it worked well before and now it wants to act up. Oh well I guess I’ll just get to wiring the fans in. Now I have to worry about the alternator.


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[gadget73]

If the drier is sweating pretty good, thats a good indicator the evaporator is fully charged with liquid. I'd be very hesitant to add more otherwise it might start getting liquid back to the compressor, which is basically instant death. Also honestly once the evaporator is fully flooded its just not going to give you any more. The pressure gets higher which means the temperature is higher, so the cooling ability drops.

Idle performance is never as good as moving performance. Less airflow, less compressor rpm. More airflow on the condenser helps a fair bit.

[87GrandMarq]

Looks like I’ll be adding fans soon then. I have a generic fuse box that I’m looking for a spot to mount for the fans and maybe headlights relay harness.


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[87gtVIC]

Looking forward to see what you come up with.

I have a high amp relay spot open in one of my under hood relay boxes and am looking for a new project.

Please document what you do if it is not too much to ask.

[87GrandMarq]

Oh for sure, I’d like to contribute something to the forum.


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[sly]

IIRC, 2x 12 inch fans will fit if you can find pusher fans to mount either side of the center core support. Maybe 13 inch fans. Been thinking of changing up the fan setup on my 93 as well and getting the PCM to control the electric radiator fan I installed several years ago.