Engine Size: 4.0
Refrigerant Type: r134
Ambient Temp: 103
Country of Origin: United States
Hello all, my name is Mark. Thanks for this resource. This is my first post in this forum.
I have a 95 Jaguar XJS that uses a Sanden sd7h15 compressor 7954 . In the last 14 months I have replaced the compressor with New aftermarket compressors twice (-First replacement went out after a few months), Dryer (x2) Expansion valve (x2) , Condenser, Evaporator, Blowers inside of the car , blend doors, fitted two spal pusher fans in front of the condenser.... all the parts I bought where from a very reputable place that specializes on jaguar parts.....My cooling sucks at idle...It just takes the humidity out of the air. If I put the car on neutral at a stop and idle from 550 to 1500 its great-otherwise its poor at stops. I do not have gauges so I can not give you the current pressures, but 4 different experienced mechanics who only work Jaguars told me the pressures are right and the system is full, however mechanic number one thinks the pulley on the aftermarket compressor is larger than the stock and it is turning slower than it should. mechanic number two thinks the compressor is weak-he reached this conclusion because after he reved the car the pressure did not come down as fast as he thought it should-although he thinks that if its underdriven then it would cause that problem. Mechanic number three wants me to use a parallel flow condenser. At this point I think the car has pleanty of ventilation at the condenser with two additional pusher fans so I have ruled out a new condenser. I can either buy a rebuild compressor by Sanden(which costs half of what I paid for the brandnew after-market one)and change the dryer and expansion valve -or-I can go on a scavanger hunt for a smaller pulley and try that out, thus avoiding the other new parts and evacuation/recharge .. Please advise!!!!!
"If I put the car on neutral at a stop and idle from 550 to 1500 its great-otherwise its poor at stops."
Sounds like a condenser airflow problem.
THe pusher fans might be roaring but have you checked to make sure the pusher fans are actually pushing the air into the condenser? If they are running backwards the airflow through the condenser would be good while stopped. Once moving though, the forced driving airflow would be against the fan airflow resulting in little actual condenser airflow and poor cooling.
Might try putting a sheet of paper in front of the grille when stopped and see if the fans pull the paper to the grille or blow it away.
Edited: Tue August 03, 2010 at 8:37 PM by ACProf
Thanks for the reply.
They have a toggle switch, so I can have them on with the car of. They push air thru the condenser and the radiator.
Well... one of those mechanics may be right.
If you have good cooling above 1500 engine rpm, then you have a compressor volume issue. The OEM compressor was a 158 cc Sanden, with a small pulley Like THIS..
If you still had the OEM part you could compare it. A larger pulley would have required either a different belt, or the tensioner is maxed out.
You can cool the condensor to 60f, and if there is not enough refrigerant flowing the evaporator will not get cold.
The pulley issue should be easy enough to rule out. Go look at yours vs that pic. It should be obvious if the larger pulley is fitted.
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Thanks for the reply
I do not think that picture is of the actual compressor since the ones for this car are single v's......But if we are just talking about size, then the v pulley on the replacement compressor(s) is larger than the one depicted.
There are several questions concerning this repair.
What occurred to the OE compressor or why was it changed?
What type 'aftermarket' compressor was utilized? Manufacturer or Supplier info.
How was the system prepared for the new compressor? Was the system totally cleaned/flushed prior to the installation of the new compressor? Was the system charged by hand or the use of a reliable recharge machine? How much refrigerant was introduced into the system. Posting pressures would be a good idea.
How much lubricant was added to the system?
The difference in size of the drive pulley can have a very serious effect on vehicle cooling, insure that there is no more than 1/4 or 1/2 in difference.
A good test should be conducted with a high stress load on the system. Max Air, High Blower, Doors open, Engine @ idle speed. This is a produces a extreme heat load on the system.
Obtain a good touch probe thermometer. Use this tool to determine the amount of heat transfer of the evap and condenser. Temp drop across the condenser should be app 25-30 degrees. There must be sufficient temp drop to insure correct change of state of the refrigerant. Flow devices are designed to flow liquid refrigerant and if the condenser does not function properly the resultant liquid/gas or true gaseous flow may inhibit evaporator cooling.
Best to obtain operational pressures and temps, then repost with info and we should be able to offer a more concise opinion of the problem.
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Thanks for your help. These are the answers to your questions to the best of my ability
What occurred to the OE compressor or why was it changed? answer-I got the car from my grandfather and (stupidly) decided to change the entire system (all items noted on first post)-Nothing was wrong with the original.
What type 'aftermarket' compressor was utilized? answer-Manufacturer or Supplier info- The supplier for both new compressors was "Jagbits.com"
How was the system prepared for the new compressor?answer- System was totally flushed when all the components where chaged and charged with the appropriate machine. When the first replacement compressor gave up the same thing took place and a second dryer and exp valve went in
How much lubricant was added to the system?-answer-With the first replacement compressor appearantly too much since when it was removed and flushed for the second compressor oil dripped out of the old dryer. When the second compressor went in I made absolutely sure that the required 3 or 4 oz went in.
The difference in size of the drive pulley can have a very serious effect on vehicle cooling, insure that there is no more than 1/4 or 1/2 in difference.-answer--the tech who has been working on Jags since Columbus sailed for the New World swears my pulley is huge. I have compared it with other cars of the same vintage and they look the same. I even tried measuring it and it seemed to be same. However the groove where the belt goes does seem to be a lot deeper on the OEM compressor
A good test should be conducted with a high stress load on the system. Max Air, High Blower, Doors open, Engine @ idle speed. This is a produces a extreme heat load on the system.-answer-The pressures where tested with the car madeto idle @1500 and the pressures where deemed to be fine, but the mechanic who claims my compressor is weak meantioned that when the idle was dropped back to the normal 550 the high side dropped slowly.
Obtain a good touch probe thermometer. Use this tool to determine the amount of heat transfer of the evap and condenser. Temp drop across the condenser should be app 25-30 degrees. There must be sufficient temp drop to insure correct change of state of the refrigerant. Flow devices are designed to flow liquid refrigerant and if the condenser does not function properly the resultant liquid/gas or true gaseous flow may inhibit evaporator cooling. -answer-I will look into geting it done
Best to obtain operational pressures and temps, then repost with info and we should be able to offer a more concise opinion of the problem. -answer-i do not have gauges at the moment, but I can assure you the pressures are fine. I have paid too many times just to have people hook up their gauges just to make sure I have not been loosing freon-never has anyone noticed the pressures to be out of range
For what its worth from the peanut gallery:
I'm thinking you may have a combination problem. You say that when you run up to 1500 rpm it cools fine but at idle which you put at 550 it's the pits?
Your Jag is supposed to have a low idle at 750. I haven't been able to find what the high idle should be at. Your shop manual should have that info.
Most of the 6's I've owned idled at 1000 to 1250 on high cool and high fan with the windows open. But some of the older cars I've owned never did cool all that great at idle. Just my experience here I'm NOT an expert.
That combined with the wrong pulley could be your problem.
If you are farely handy it would be worth the money to pick up even a cheap set of harbour freight gauges and measure it for your self. If you are going to multiple mechanics to get it checked, I'm inclined to think that you don't really trust or have a track record with any of them. You can get a set from as low as 29 (on sale) new to 200 depending on the bells whistles and brand name. Or if you have your heart set on something special do a pawn shop crawl but I wouldn't do one unless you KNOW what your looking at.
If you can give them some hard numbers these folks are more than willing to help.
Good luck and I hope this gives you some ideas:
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In my opinion, if you're going ot invest in some tools. Get somehting that you can trust is providing you the correct information.
Mastercool AC Gauge Set
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