"NO MAS" - Rear A/C cooler than the front
#16
Did you clean the front evaporator? Those have a history of being clogged up. See SeanR's thread A/C not cooling well? Evaporator cleaning for a rather extreme case. Also see the "How To" HVAC blower removal and clean-up + Cleaning the Evaporator.
Edit: ahhh... I see that Maine just beat me by a few minutes on this suggestion.
Edit: ahhh... I see that Maine just beat me by a few minutes on this suggestion.
Last edited by Ed Scherer; 08-21-2015 at 05:48 AM.
#17
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IR guns give very poor air temp readings. Instead, grab a [couple] little digital thermometers with stick probes, us thm in the vents. From the Grocery store kitchen section, Wal-Mart, etc.
Then it's not the heater valve leaking by.
I ordered another rubber manifold that connects to all 5 solenoids. Gonna check the auto vent adjustor under the dash & glovebox. Trying to get it cold for Memphis to DC trip at the end of the month.
You can test that from the engine bay, right where the little check valve connects by the brake booster. Use your MitiVac or similar, you should be able to pull (and hold) a vacuum there. Takes some pumping since you are also pulling air from the accumulator in the fenderwell, but that really tests everything at once. If you can't get or hold vacuum there, go to the rubber manifold by the chackvalve and do each branch one by one to find the leak. If you can't hold at the HVAC tube there, but can at all the individual solenoids, only then should you suspect that rubber manifold at the solenoids.
Even on low speed first thing in the morning air is noticeably warmer than rear.
I ordered another rubber manifold that connects to all 5 solenoids. Gonna check the auto vent adjustor under the dash & glovebox. Trying to get it cold for Memphis to DC trip at the end of the month.
#18
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From: Rep of Texas, N NM, Rockies, SoCal
MIne is the same, and I've decided that the specs on the evap expansion valve in the front is set higher than the one in the rear. Since the one in the front is always on in AC mode, they set the exp valve pressure/temp gradient slightly higher than the rear. Also, there is natural heat soak in the firewall from the hot engine radiant heat that isn't present in the rear.
It's just never going to be as cold in the front unit unless the exp valve is replaced with a lower one, then you run the risk of freeze clog. I've cleaned the fins, tied off my heater valve, made sure the recirc flap was up and tight, and it's still ~10-15F warmer in the front. So, I run the front unit on 3, and the back unit on 2 until I get the right temp then I lower the back unit to 1 setting and the front adjusted to the best conditions.
It's just never going to be as cold in the front unit unless the exp valve is replaced with a lower one, then you run the risk of freeze clog. I've cleaned the fins, tied off my heater valve, made sure the recirc flap was up and tight, and it's still ~10-15F warmer in the front. So, I run the front unit on 3, and the back unit on 2 until I get the right temp then I lower the back unit to 1 setting and the front adjusted to the best conditions.
#19
Yeah the heater control valve on these cars *sucks*. As in, doesn't hold water even with good vacuum. I'm on my 3rd or 4th replacement in 4 years, I lost count.
To zip-tie it don't you have to remove the air box? Yeesh.
To zip-tie it don't you have to remove the air box? Yeesh.
#21
I've tested all vacuum parts using Pirtle's & Dewayne's guide. I will clean the evaporator. Onece I get the solenoid manifold changed out and clean the evaporator & recheck for leaks, if it still doesn't cool correctly, I'll get the freon amount professionally measured.
Good info to know about expansion valves. If I can't get it colder, it'll be strictly a winter, spring, fall car. Memphis heat to much w/o good air.
Good info to know about expansion valves. If I can't get it colder, it'll be strictly a winter, spring, fall car. Memphis heat to much w/o good air.
#22
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From: Rep of Texas, N NM, Rockies, SoCal
Cleaning around the temp sensor in the evap may have a decent affect on lowering the temp setpoint of the exp valve. If it is the variable type that senses the evap core temp(and I think it is) then having it clean could allow the setpoint of the exp valve to go down near freezing. It sounds like from the link from Sean several people have improved their front cooling by cleaning in there.
#23
I remember when my neighbor in Chicago was flabbergasted that I had a choice between spending extra money on painting the car or getting the AC fixed, and I chose painting the car.
#24
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Cleaning around the temp sensor in the evap may have a decent affect on lowering the temp setpoint of the exp valve. If it is the variable type that senses the evap core temp(and I think it is) then having it clean could allow the setpoint of the exp valve to go down near freezing. It sounds like from the link from Sean several people have improved their front cooling by cleaning in there.
For sure I'd look at how clean the front evaporator is. They can get full of dust, and that turns into a mud cake if you live in a humid climate where a lot of the cooling is spent condensing moisture. SeanR's thread on evaporator cleaning is a great guide.
At the same time, take a look at the sight glass in the top of the receiver/dryer, and see if there's a pretty solid liquid stream flowing there with the system engaged and engine speed about 1500 RPM, fan speeds on 2. There should be only a small amount of bubbles/foam passing through under the glass. If there's a lot the system may be undercharged or have air in it. Charging only by the sight glass isn't a great idea, as you really need to have pressure gauges to read high and low side pressures, and thermometers to tell you how and how much heat is being moved.
FWIW, I seldom if ever bother to use the rear air, even when I was in always-sunny SoCal with a black car and a greenhouse riding in the back all the time. It's there for local comfort of rear seat passnegers, and does not appreciably speed the extraction of heat from the cabin vs. front system only. The system is condenser limited, that is the limitation on total heat moved is at the condenser in the front of the car. Turning on the rear system will always reduce the flow and therefore the heat removal capacity at the front system. Meanwhile, the rear system has no heat migrating through the firewall or absorbed through the dash. No heater coils right next to it to share migrating engine coolant heat. No possible misadjusted or non-sealing blend doors or fresh-air doors bleeding heat into or around the AC evaporator as the front system does.
Greg Brown has shared a few tips on airbox maintenance over the years, and has identified some of the failing blend door seals as offenders in the war for cold AC. He's done a few hot-climate system mods that add more condensing capacity with heat exhangers and fans under the headlights, and spends time rebuilding and resealing the airbox in front to make sure everything works as originally intended there. These cars were developed with testing in seriously hot climates, and the factory had a bit of experience with trying to sell rear-engined air-cooled cars with no or at best marginal factory systems installed. They knew that folks in many of their markets were sensitive to HVAC performance, so the 928 system is in fact overdesigned for the size of the (subcompact) car cabin. Getting everything back to at least the way it was delivered is a big first step in any AC performance effort.
#25
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From: Rep of Texas, N NM, Rockies, SoCal
Most TXV are not user adjustable, but one could find a repl TXV and capillary with a more aggressive flow rate that would cool the evap core better. Just a few thoughts, but I haven't dug into it enough to say for sure.
#26
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Hmmm. The TXV on my car has a very short cap tube into the return side of the block. Never makes it actually into the evaporator, only reads discharge temp into the suction line.
It's been a while since I had mine apart, about 18 years, but my feeble memory is that the configuration of the expansion valves is the same front and rear.
It's been a while since I had mine apart, about 18 years, but my feeble memory is that the configuration of the expansion valves is the same front and rear.
#27
Since I just cleaned my front evaporator a few hours ago, here's yet another example of just how bad those can get. I'm pretty sure I've seen worse examples (well, better examples of extreme fouling!), but this is still pretty bad. The two giant dust bunnies in the foreground were a bit surprising. Where the heck did those come from? I somewhat suspect mice might have been involved, but is there actually a path that will get them in there?
(see also my separate post on this task)
(see also my separate post on this task)
#28
Wow! Thats ugly.i looked at mine briefly and it appears to be relatively clean. I'll get a can of foam and hit it anyway this weekend. Thanks for the responses. When the part arrives, I'll get it put back together and report back.
#29
FWIW, I seldom if ever bother to use the rear air, even when I was in always-sunny SoCal with a black car and a greenhouse riding in the back all the time. It's there for local comfort of rear seat passnegers, and does not appreciably speed the extraction of heat from the cabin vs. front system only. The system is condenser limited, that is the limitation on total heat moved is at the condenser in the front of the car. Turning on the rear system will always reduce the flow and therefore the heat removal capacity at the front system. Meanwhile, the rear system has no heat migrating through the firewall or absorbed through the dash.
#30
Alan