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1987 Mustang A/C Issues

Porkchop on Wed April 08, 2015 4:23 PM User is offline

Year: 1987
Make: Ford
Model: Mustang
Engine Size: 302
Refrigerant Type: R134A
Ambient Temp: 75
Pressure Low: 40
Pressure High: 255
Country of Origin: United States

I've got an 87 Mustang that I'm working on for my Dad. I'm not sure if I've already asked this question here or not, if I have, I apologize.

Ok, the car has had a brand new evaporator core installed in the dash. Every line on the car has been replaced, including the liquid line containing the orifice tube. The compressor is brand new. It's had the condenser upgraded to a parallel flow condenser, though the same issue was happening with the standard factory replacement piece. Basically, every single piece of the system has been replaced, the liquid line has been replaced 3 times and the results are the same.

A vacuum has been pulled on the system, refrigerant has been added by reducing the required amount like you're suppose to if you're doing a R12 to R134a conversion. I've tried with less refrigerant and with slightly more, the results are the same either way. It doesn't really matter what the ambient temp outside is, it can be 65 or 85, it doesn't make a difference. It pretty much makes no difference what the low side or high side pressure reading is either. You crank the car from a dead cold engine, vent temps might be at 60 degrees... far from desirable. Cut the car off... wait 5 minutes or 5 hours... crank it again and you get a totally different temp from the vents, it may be slightly colder or warmer... depends on the mood the car is in I guess.

It might be cooling at 60 degrees at idle and you can drive down the road, it usually goes up in temp but sometimes it may fall, to say something like maybe 55. Sometimes, it goes up in temp to like 70 degrees. I have tried adding and reducing the amount of the charge, nothing that I do changes and makes this system cool. I have also carried it to several different shops, they've tried the same things and got the same results. I feel like the liquid line that has the orifice tube is designed for R12 and it's possible that I need to change to an orifice tube for R134a, is this possible? I have a 2004 Sterling LT9513 that use to idle with temps at around 40, doesn't now but that's a different discussion. I have a Honda Odyssey mini van that will idle with temps around 40 or so, so that tells me that R134a will cool at idle and certainly while driving down the road. I just can not get this car to cool at idle and most of the time I never see anything cooler than 60 while driving.

It cooled perfect with R12. Developed a leak and ended up converting to R134a, had this problem since. Decided to buy all new parts, no difference, still no cool. I guess I should have ponied up the cash for R12..? Is it possible that the compressor is just crappy and needs to be replaced even though it's new? Or is it in the orifice tube and buying the repair kit and changing orifice tube size is what I need to do? I have no idea what tube size I'd need though, the blue or black or maybe even another one totally different, how do you figure what orifice size to use?

Dougflas on Wed April 08, 2015 5:10 PM User is offline

Try to bypass the heater core. You may be getting a reheat thru the heater. Measure the temps of the input and output f the evap with the engine at 1500 rpm's. The pipes should be the same temps or the output slightly colder. If they are, stop adding or removing refrigerant. You're close enough to get good results; if the vent temps still aren't satisfactory, look for door flap problems. Also, mist the condenser with a water hose. If the high side drops like a rock, you have condenser airflow problems.

mk378 on Wed April 08, 2015 8:18 PM User is offline

Does the compressor cycle at all? Does the evaporator output and accumulator tank get cold-- if so, how cold? Should be near 40.

Porkchop on Fri April 10, 2015 3:22 PM User is offline

Sorry for the delay, I work at night and I've not had much time during the day.

The heater core has been bypassed, no difference was noted. I don't really have a great thermometer to measure those temps on the core, I get around 70 degrees but the vent temp reads about 60, sometimes 55. I've also tried misting water on the condenser, that didn't really seem to make any difference either, as does riding down the road (doesn't help). The compressor never cycles on a Ford, if it cuts off, it does so because the freon/refrigerant is low. There is no high pressure cut off, only low cut off. I've never owned a Ford that cycled, my Sterling dump truck is basically a Ford and it never cycles either.

The lines will sweat up, they do seem cold or cool... I'm going to try to work on this car again tomorrow and get some better test/results to post here. I'm really thinking it needs a different orifice tube. I believe the liquid line is set up for R12 and hence the orifice tube is designed for R12. But I don't know a whole lot about AC systems, so I'm asking you guys for help.

Dougflas on Fri April 10, 2015 7:11 PM User is offline

If the "pipes" on the evaporator measure 70*, that is not good. Most digital voltmeters have a wire type sensor to measure temperature. Take the sensor, tape it to the lines and insulate it. They need to be close to the same temps. This tells you the evaporator is filled with refrigerant which is what you want. Actually, the output "pipe" should be slightly colder. When you misted the condenser, what was the pressure difference from when it was dry?

mk378 on Sun April 12, 2015 11:00 PM User is offline

Put the interior blower on low or unplug it entirely and see if the low side comes down. It (like most American cars) is a conventional CCOT system which will cycle if the low side ever gets to 25, which it needs to to have good cooling. If the low side won't come down even with no heat load, you have to consider that the compressor is worn out or a dud.

You should run the same charge weight specified for R-12 unless that causes excessive high side pressure, which it really shouldn't with PF condenser and fan clutch in good condition. Never use more 134a than you would 12, that is definitely going to be overcharged.

Edited: Sun April 12, 2015 at 11:01 PM by mk378

Porkchop on Sun July 19, 2015 11:24 PM User is offline

Porkchop on Sun July 19, 2015 11:42 PM User is offline

OK, here's an update and I still can NOT get this car to cool...

New parallel flow condenser, ordered from Advance Auto. Complete o-ring kit, ordered from FoxResto. New compressor. The liquid line on these cars houses the orifice tube, originally on the R12 system I believe this orifice tube was blue but I'm not 100% on that. According to all information I can find, that would have been the correct color for this car. I got an orifice tube repair kit, basically lets you cut the line and install this do-dad and put whatever orifice tube you want into the system. I have a 2004 Sterling LT9513 that came with R134a, uses a Ford black & white orifice tube, so I tried this tube on Saturday.

Ambient air temp - 85
Low side PSI - 35
High side PSI - 225
Vent temp - 70

This was at idle, at 1500, at 1800 and at cruising speed of 60 mph. No matter what, vent temps didn't vary much from 70. The charge in the system was 3 - 12oz cans, about 36 ounces, the car calls for 2lbs, 10oz. There is a 14" Hayden fan that runs with the AC on this car, I added it also as I added one to my truck and I can get vent temps of 38 degrees in that truck before the system just freezes up.

So, today I switched to the BLUE orifice tube. With one can, 12oz, in the system I already had almost 30 PSI on the low side. With the same charge of 36 ounces in the system...

Ambient temp - 87 degrees
Low side PSI - 35
High side PSI - 300
Vent temp - 59 degrees

So at this point I was very disturbed, took a water hose and ran over the condenser. The high side pressure dropped to about 150 lbs but I didn't check the low side readings, I know I should have. The temps at the vents however didn't change, stayed at 58-59 degrees. Drove the car down the road, same thing... about 60 degrees out the vents.

There is SUPPOSE to be a new evaporator in the dash, the accumulator has been changed, the pressure switch has been replaced 3 times but no matter how I adjust that screw in it, I can not get it to turn the compressor off. It will engage the compressor with the system completely empty, I have NEVER seen a Mustang that will cycle the AC compressor though... NEVER and I've owned a pile of these cars, this one is my Dad's. My Sterling truck, it doesn't cycle the compressor unless it's low on refrigerant. It appears to me that there is some sort of obstruction in this AC system... but where? Every single piece has been replaced by me personally. I have flushed every line on this car with AC flush under high pressure, what couldn't be flushed has been replaced at some point in time. The system has been vacuumed every time it's been opened, down to 29-30 on the vacuum gauge. The system holds a vacuum. I do not know what is wrong with this AC system on this car. Does anyone have any other ideas?

Also... the blend door is closed, I checked that Saturday. As best I could get, the temp reading on the discharge side of the evaporator has been a best of 44.5 degrees but I've seen nowhere near that temp in the vent. The vent temps will be the same, the system readings will be the same whether the car has ran for an hour or if you just cranked it from sitting overnight. So in my opinion, the engine temperature doesn't matter but I still checked the blend door. I have also clamped off the heater hoses, that made no difference either.

Porkchop on Sun July 19, 2015 11:53 PM User is offline

OH, forgot... most Mustangs I've found listed has used an orange orifice tube. So again today (Sunday), I just pumped it down and replaced the blue with the orange. The ambient temp and low side readings stayed the same, the high side went down to around 250 or so and running water on it brought that down to 150-165. I got the coolest vent temps previously with the orange tube which were at one time, 45. But sometimes it'll have low pressure readings and then sometimes you'll get high readings. It's not blown very cool air in awhile, regardless of what I've done.

Dougflas on Mon July 20, 2015 1:36 AM User is offline

By any chance, is there an orfice tube in the evaporator? You do not want to run 2 metering devices.

Porkchop on Mon July 20, 2015 11:24 AM User is offline

No sir, only that one. It's driving me bonkers.

jsmitty on Mon July 20, 2015 11:36 PM User is offline

To me it sounds like your chasing a refrigerant problem when you should be looking at a blend door problem. If the line going into the evap, and the line coming out are both cold (or outlet is colder) & sweating in humidity, then the system is working as it should. I believe your sending heat into the vents via another path, instead of through the evaporator. There could be a door that is flopping around while driving due to a failed servo, or a vacuum issue (possibly a leak) that's causing intermittent vacuum. There's a spaghetti mess of vac lines running under the dash, and across the engine on these cars - plenty of places to leak from ...

Doesn't matter what brand the vehicle is - all CCOT systems will cycle when the low side pressure gets low enough. My Grand Marquis shares many similar parts with the Mustang, and it will cycle on lower fan speeds after the cabin cools off, or at any fan speed on cooler days. During the hot humid weather the Northeast has been having, it cycles very little, if at all. Not cycling means there's a large heat load, an inadequate condenser (or airflow across it), or it's overcharged (or the cycling switch is adjusted to trip at too high a pressure).

Another problem I find up here alot is mouse nests. Not sure how the evaporator is set up on the Mustang, but some cars they love to build nests in that compartment. You would notice either the smell or reduced airflow though. I've also heard of someone forgetting a shop rag inside after a heater core replacement. That makes for a bad day!

The evap on the Marquis was accessible from under the hood with the right fender well removed. After almost 30 years of use, there was very little debris in the OEM evaporator, surprisingly. With the evap out, I noticed a blend door not closing all the way. I bent it until it did. System has been working better than ever. Could have used new seals around the blend door. Maybe next time .. hopefully over 10 years from now.

Edited: Mon July 20, 2015 at 11:37 PM by jsmitty

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