Ac Issues

[87GrandMarq]

I noticed that the ac has not been great during the day on my 90 mgm. Yes it is hot and it’s Florida but my 87 works great even in the heat. So I got a new set of manifold gauges and got to work. The ambient temps yesterday late in the day were about 85* with close to 100% humidity. The pressures I got were strange. After about 5 minutes or so when everything was stabilized I got 53 psi low side and 350 psi high side with a discharge temp around 65*. I revved it to probably around 2k rpm’s and kept it there. The low side got down to about 30 psi and the high side climbed to almost 400 psi. Discharge temps lowered maybe 5* or so temporarily, then it went back to where it was before. Now after about 10 minutes, out of the blue the low side started dropping and got down to about 30 psi and stayed there and the high side lowered to about 225 psi and stayed there. The discharge temps got to around 50* or so. When the sun went down it had no problem getting into the 40s even though it was probably still about 80* and muggy. I also noticed that the blend door doesn’t open up. When I open it manually it stays there and the temperature drops 5*-10*. I’m pretty sure that’s just low vacuum so I’m not worried about that but I thought I’d add it.

As I write this post I’m sitting in my 90 with the ac at full blast in 91* heat with high humidity and it’s steady at about 63* at the vents after 20 minutes or so. It was at 75* for a while but dropped.

I’d be inclined to think it’s a heat soak problem since there is only a mechanical fan to draw air at idle but the fact that the discharge temps don’t keep climbing at idle would contradict that right? Thoughts?

[matth825]

Elevated low and high side pressure are usually condenser airflow related. How's your fan clutch? If old/high mileage replacement would be warranted. If you can get a heavy duty one that's even better as you'll get higher fan speeds.

How does the condenser look? Is it dirty? Lots of bent fins from impact damage?


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[sly]

That is an odd problem. At first I was thinking maybe the system had too much gas in the system, but then it went to normal pressures. Either the compressor is doing some really freaky things with the piston seals or the orifice tube had some weird clog that cleared. I'm leaning towards the compressor doing weird stuff since the orifice tube being clogged would make high pressures on the high side but would short cycle the low side as it would draw it down below 15psi.

[87GrandMarq]

It never cycles it’s always on, I don’t know if I added that. But I’d tend to agree there’s something up. As far as the mileage goes I don’t know. The carfax said there was a discrepancy so I don’t really know. Could be high 100’s or low 200’s. Either way it runs well and doesn’t smoke, burn oil or make any noise so I’m thinking it’s on the lower end. And the condenser looks good. No bent fins and I cleaned it out with a garden hose last night. Someone converted it to r134a before I bought it. Who knows how good of a job they did.

[gadget73]

oof, 400 psi! Thats way too high. Shouldn't see over about 300

sounds like not enough airflow across the condenser to me, usually bad clutch fan is to blame, but missing shroud or the condenser just being packed full of dirt and dead bugs will do it too. If cleaning is no help, I'd really be looking at that fan clutch

[87GrandMarq]

I’ll start it up and check the clutch just to make sure. It could be slipping, I haven’t checked it.

[87GrandMarq]

Gadget I think you’re right about the clutch. After turning the key off the fan will keep spinning for another four or so seconds. I’ve never noticed this before and pushing it by hand it stops pretty quickly. Not very scientific though.

[DerekTheGreat]

I once had a Ranger which cooled about effectively as warm piss tossed on your forehead. Turned out there was indeed a bunch of garbage jammed between the condenser and radiator, once fixed, it worked great. The engine never overheated, though. Although I was only 19 or so when I had that thing, I don't think I was paying a whole lot of attention to that.

[87GrandMarq]

I can take a hose to it again just for fun I guess. I mostly got water in the condensor. Anyone have a part number for a heavy duty fan clutch? I bought one for my 87 on eBay and it works well but it’s a no name brand. All I can find are standard duty. Also are they thermal or non thermal from the factory?

[jaywish]

3 or 4 seconds means it is shot. 100%

[Tiggie]

Thermal. YB-327 is the Motorcraft heavy duty. There is one on eBay currently but it's kind of high IMO. YB-328 is the standard. I put the 327 on my wagon and you can hear it in action at the appropriate times.

[friskyfrankie]

Appears that "YB-327" is coming from Israel (from the price conversion info).

[87GrandMarq]

I sent an offer, we’ll see. If that doesn’t work out is there an alternative? The one on my 87 is great but I don’t know the brand and doubt it’s motorcraft.

[jaywish]

Peraps try your flaps and see if they have any heavy duty that could be ordered.

[Tiggie]

I have a Hayden 2710 on my other wagon. It does fine with keeping the car from getting hot. It probably does all it needs to, but that car does not have functional A/C. The 90 wagon with the YB-327 does have air and that clutch really kicks on and sounds like a tornado under the hood. But I wouldn't pay silly money for it; the Hayden gets the job done.