1991 ZR-1.

At best, I get 58-59 degree temps from my vents, given 85-90 degrees ambient temp, this is on recirc, and after at least a 20 minute drive. Even on longer drives, I haven't seen much lower than that.

Today in my driveway, I connected my gauges.

With a garden hose spraying the condenser, the low side will get down to the 28 psi range. Without the hose, the lowest was about 37. It's about 90-92 degrees ambient plus heat emanating from the engine compartment at idle.

I didn't focus too closely on the high side -- but without the hose it was 250+, with the hose I think it was around 175 or so.

A thermometer placed into the blower box, where the resistor module is located, yields 42 degrees as the lowest observed temperature.

Looks like there's a problem outside of the refrigerant plumbing, if there's 42 degree air coming off the evap but 58 degrees at the interior vents, yes?

I did not want to add or remove any refrigerant (R-12, by the way), since it seems like 42 degrees from the evap is pretty good.

The door that blocks off the heater core appears to be functioning properly, looks sealed to my eyes at least.

Where to go from here? disassemble dash to look for problems with ducts?

Or just suck it up, and accept that this is the best the system can deliver?

Additional info added:
Using the C68 display, parameter 34 shows that at 60 degrees selected, plus recirc, the requested temperature door position is 253 (full closed). However, parameter 31, which shows the temperature door travel range, shows 184, when in fact 200 is apparently full-closed, so it looks like for whatever reason the control head is reporting that the temperature blend door is actually NOT in the full-closed position. Hmm.

Also, another interesting thing, is that parameter 1, which is the temp setting (shows 60-90 range in the chart, just like the selectable temps), shows 64 when in fact I've got it set to 60.

Now I'm more confused than before.

Also, after I shut off the A/C via the control head, and the pressures equalize, the compressor clutch didn't fully disengage - the center of the pulley was still rotating at about one revolution every 3 seconds. I can't say I've ever noticed this before. Is this symptomatic of something? I'm guessing it's just due to pressure equalization in the compressor...



Thanks
Andrew

 

I verified that the temp blend door is definitely going to full-closed when 60 degrees is selected. The door closes against its stop, then gives one more clunk as if to indicate that the actuator hit its internal stop.

Interesting observation:

I removed the blower motor, to verify that the recirc door is indeed closing completely - it appears to be. By removing the blower motor, I can see the aft edge of the evaporator core. Interestingly, there's about a 1cm gap between the end of the core, and the firewall. Seems like this would lead to air bypassing the core and making its way into the ductwork. My measured temp in the blower box was taken further forward, where air was going through the core rather than around it.

I'm going to try to seal up this area.

 

I'm sorry to say I don’t have a good suggestion at this time. But your problem sure has similar symptoms to this thread. I don’t know if the solutions are going to be related. But just thought of this with your information.

http://forums.corvetteforum.com/c4-t...rator-box.html

Packing and insulation can deteriorate over time. Would not be the first time it happened.

 

I sealed the gap between the evap core, and the firewall. Also sealed a smaller (3mm) gap at the forward edge of the evap core where it meets the blower box housing. This IS an aftermarket evap core, and I didn't have the original to compare dimensions to, so it's likely that it's either smaller than it should be, OR the original had foam strips to make up the difference.

Anyway, I put it all back together, and with no other changes, this made an 8-9 degree difference. I saw a low of 49 degrees at the center vent, with all other vents blocked, 89 degrees ambient temp, sitting in driveway with hose on condenser and engine at 2000 rpm.

One other thing I may look into -- the intake for the recirc is basically buried in the dash, with no way for cabin air to get back to the blower. I may modify the RH hush panel to allow for more airflow into that area, in an effort to improve the efficiency of recirc mode.

 

Another thing I found as I'm reassembling things, is that the foam that seals the junction between the ductwork and the dual vents under the glovebox, is too thin to be sealing fully. I had replaced the original crumbly foam with some generic stuff from Lowe's, but what I chose was too thin. I think I need to use at least 3/4" thick foam in order to prevent air leakage into the dashboard rather than coming out of the vents.

 

Pics of evaporator gap:

As seen from blower motor housing:





As seen from blower resistor access panel:

 

Your Pressures sound ok, is the rad area clean, free of debris?

49 is better but 40 is more like it.
Maybe your compressor is just getting tired. Worn out. It does happen.

My 93 will freeze you right out, so cold I swear it'll form ice cicles somewhere but never does.

 

Compressor has about 11k miles on it. Remember, this is a ZR-1 we're talking about here, whose A/C system has less cooling capacity than the base C4.

A tired compressor should be reflected in the pressures on the gauges, no?

Condenser is free of any debris.

 

I thought of that after I posted it. Maybe 49 is the best it can do.

Your right on the compressor being tired.

Hmm....you did take care of the aftermarket Evaporator so that is fixed.

Honestly, I think you covered your basics. I see nothing that stands out to me. I'm used to a bit lower low side pressures than 37 but its not really bad or anything. Considering that was at idle in 90+ ambient probably not too bad.

Air at evaporator being 42 sounds about right, so maybe that is all she wrote?

If you got 49 sitting in your driveway, with a wet condenser, take it for a ride and see what your duct temps are. I would not consider 49 to be out of the ball park for the conditions...hot, ZR-1, no airflow,etc...

 

Yep, going to replace the foam on the RH side tomorrow, then take it for a test drive and record center vent temps. Will report back with results Thanks for your input!

 

The foam that seals the ductwork is usually gone after the warranty and duct tape (or whatever you can find at Home Depot) is the best alternative I've found. The early C4's seem to end up with air streaming pass the ECM and not out of the vents. Also be sure to seal the Defrost Vent where it joins the heater box.

If the you think the Temp Door isn't closing; try to keep it shut with a screwdriver or something and see what happens.

Follow a Pressure/Temp Chart for R12 (or whatever gas you're using) when determining center vent temp and be realistic about it or use the design estimate in the Service Manual. 30 psi is 32 degrees and if there's 6 to 8 degrees of superheat, that's a 38 to 40 degree evaporator temp which is really about average; maybe better than average. 38 to 40 degrees at your knuckles is numbing and uncomfortable and either requires a 60 degree inlet which is rarely possible once it's much over 80. Ie; you're more likely to see those temps on a 60 degree day and after a couple of minutes, move the vent off your hands or crank in some heat so you can get the feeling back.

Face plate still spinning or slipping with the pulley can mean that the air gap has gotten too tight - should be .020 inch. Re-shim if it's worn down - shim kits are about 12 Bucks or if it's a press-on; you'll have to buy a special tool (though those models often increase in gap and have to be pressed in closer). Your compressor would otherwise seem ok.

For those that have one, use the solid top.

 

Thanks for all the tips! Duct tape isn't going to work for the vents in question, since there's no access to tape around the joint when the vents are installed.

That's why I need to use foam to bridge the gap between the duct and the vent diffuser.

 

Just went for a test drive -- WOW what a difference! Like SunCr said, it was almost uncomfortable having low-40s air blowing on my knuckles. The thermometer was indicating around 43-44 degrees, after a couple of miles on the interstate. In stop and go, I was getting around 50 (whereas I used to get more like 60-62).

I'm a happy camper!

 

Glad it's better!

 

Awesome. VetteMed, thanks for taking the time to post the details and results. This was valuable information.

 

Fixed one!!