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'97 Town & Country rear air not cooling

webbch on Mon June 11, 2007 8:54 AM User is offlineView users profile

Year: 1997
Make: Chrysler
Model: Town & Country
Engine Size: 3.8L
Refrigerant Type: R134a
Ambient Temp: 88 F
Pressure Low: 41 psi
Pressure High: 240 psi

The rear vents are not providing cool air, although the front ones are OK. This was my first time checking pressures, and I had the A/C on max cold, both front and rear blowers on high. My altitude is about 3500 ft, and the ambient was about 88 F at 2 inches in front of the condensor, no fan blowing on it or anything. All temps measured with the thermocouple on my multimeter. I forgot that I was supposed to check these at an engine rpm of 1500, so these pressures and temperatures were checked at idle (1000 rpm)

The front vent temp was 61, the rear vent temp was 84.

Reading through other threads, the most prevalant problem seems to be either a mode door actuator or a clogged TXV. Is the low side pressure a tad high for these conditions? Are these the symptoms of a clogged TXV in the rear? Thanks.

Chad

iceman2555 on Mon June 11, 2007 10:00 AM User is offlineView users profile

The first step and most important is knowing how much refrigerant is in the system. Suggest to have the system recovered/evap for app 20 minutes, and recharge with the correct oe spec of refrigerant. Adding an 1-2 oz of lubricant may also be done at this time. Dye is you like can also be introduced into the system (1/4 oz is sufficient).
Once this is done, retest pressures and temps and post info. The service may rectify your temp problem.
Good luck


-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

webbch on Mon June 11, 2007 12:47 PM User is offlineView users profile

I understand the importance of knowing how much refrigerant is in the system. However, it seems very counter-intuitive to me that a low charge could produce relatively good cooling up front and virtually no cooling in the rear. Wouldn't a low charge tend to affect both systems, i.e. both front and rear would be cooling poorly?

iceman2555 on Mon June 11, 2007 1:51 PM User is offlineView users profile

An old adage...."Ya cant pump whatcha ain got!!!" Low refrigerant charge will effect the cooling of each unit, however, it is normally the secondary unit that suffers first...extra length of tubing, movement of lubricant etc. Get the system charged properly and then test pressures. Pressures are a diagnostic tool and the first step in diagnosis of a system is knowing how much refrigerant is in the system. All diagnostic/test pressures should be based on the knowledge of complete system refrigerant recharge. Topping off a system today is an 'hit and miss' scenario at best. Even for a 'seasoned' tech it is a 'guesstamation'. Know the conditions of the system. Recover, evap and recharge to specs. Remove as many variables as possible and thus diagnosis of a system becomes quite simple.
When servicing a front/rear system, we always balance the front system in the beginning and then adjust for activation of the rear system.


-------------------------
The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

webbch on Tue June 12, 2007 11:51 AM User is offlineView users profile

OK, will evacuate and recharge this weekend to see where we're at. Thanks.

Chad

webbch on Fri June 15, 2007 4:58 PM User is offlineView users profile

OK, evacuated and recharged to see where I was at. Due to some goofs on my part during recovery, I failed to get a measurement of the weight of refrigerant recovered. Some will frown on me for it, but I used the dry ice method to recover the refrigerant, and it seemed to work quite well. Then added three 12 oz cans to the recovery tank to make sure I'd have enough to put back in the necessary amount (I have the DIY kit and and the refrigerant scale). I put in some dye, and pulled a vacuum for 30 minutes. When I recharged, I made sure I put in the required 48 oz of refrigerant called for in the service manual.

When putting the refrigerant back in, I had to rev the engine a bit in order to drop the low side pressure enough for the last few oz. of refrigerant to flow from the recovery tank back into the system.

Anyway, after it was all said and done, I checked my pressures at 1500 RPM at an ambient of 81 F. This time I got 35/320 psi for the low/high sides, respectively. Front vent temps are down to 36 F and the rears are down to 41 F, which is quite satisfactory.

So iceman was absolutely correct about needing to be certain about knowing how much refrigerant is in the system. Apparnetly, even the front vents weren't cooling up to par before this.

The other minor goof I made is I didn't wait a long time to see if the vacuum was holding, as I was concentrating on switching hoses, purging, etc. So we'll see if it holds. If not, the system has dye in it, which should hopefully make it easier to spot.

Thanks again for the help.

Chad

webbch on Tue July 08, 2008 12:27 AM User is offlineView users profile

Here we are, just about a year later now with the same vehicle, and I suspect that I may have a VEERRY slow leak, as I took the same measurements with the engine @ 1500 RPM:
Ambient Temp: 81 F
Vent Temp: 54 F
Low side: 32 psi
High Side: 265 psi

The first thing I need to do is check out the cooling system, as my wife reported that it was inching up to about 3/4 of the way to hot while driving on the freeway the other day. I was not able to replicate the overheating in my testing this evening (81 this evening, as opposed to the 110 the other day). Thus far, no coolant leaks have been found as the cooling system holds pressure. The radiator fans are coming on when I turn on the A/C, and they don't feel tight or locked up. The water pump is a little over a year old. Since the overheating occurred while driving on the freeway, I honestly can't think of anything other than the water pump or thermostat that would contribute to this (other than physically clogged heater hoses). Any other ideas on how to improve cooling are welcome - already have a tranny cooler integrated in the radiator, but considering adding an external one as well.

I've been wanting to pull the radiator and condenser to blast out all the road debris, although spraying the condenser with water didn't drop the pressures quickly, so I doubt that's a major problem with the A/C's lack of cooling. I've thought about putting in a parallel flow condenser, but looking through the grill at the current condenser, it kind of looked like a parallel flow design already - it at least didn't have one tube snaking back and forth with fins attached that I associate with the "tube and fin" type condensers. The nice thing is that ackits.com appears to have a drop-in replacement for my condenser that is a parallel flow design.

I plan to recover the refrigerant to determine how much has been lost in the last year. Regardless, it's a pretty darn slow leak to not rear its head for over a year. The A/C is still cooling OK, but not great. Any ideas on how to find such a slow leak? I've got a micron gauge on the way to help determine the severity of the leak, nitrogen and R134a for pressurizing the system, and an electronic leak detector (TEK-Mate), all of which I really have no experience using effectively - any tips for finding this kind of slow leak? I plan to evacuate the system, pull a vacuum, charge a small amount of refrigerant into the vacuum (couple of oz??), then pressurize to about 150 psi with the nitrogen and go searching with the leak detector.

Any tips or pointers are welcome. Thanks

Chad

Edited: Tue July 08, 2008 at 12:31 AM by webbch

mk378 on Tue July 08, 2008 1:34 AM User is offline

Start by looking for dye, using the UV light and the yellow goggles. It works better at night or inside a darkened garage.

The present charge can be used with the electronic detector. The Tek-Mate is very simple to use. Switch it on and after it warms up it will start to beep at a steady rate. Uncap one of the service ports and hold the detector near there to test it. There is always some refrigerant under the cap, that is not a malfunction. Actually you should sniff the service ports first without taking the caps off to make sure they don't leak. Then sniff all connections, evaporator drains, etc. The compressor shaft seal can be tested more extensively by taking the belt off and put a plastic bag over the front of the compressor. Wait a while and sniff inside the bag. Remember that R-134a is much heavier than air so it is more likely to be found below leaks.

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