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Discussion Starter · #1 ·
Today I had the AC system re-gassed as it was not working.
Apparently it is now working fine with no leaks, however the air coming into the cab is not as cold as it should be.
According to the tech it appears the heater is still circulating, so cancelling out  the cold air somewhat.
In order to figure out what is happening, I have a few questions on how the AC and heater work on a first gen.
On the controls there is a "heat button", an "AC" button and an "AC MAX" button, amongst others.
Above these there is a slider cold to hot. I understand the AC button but why is there a heat button?,surely this is controlled by the slider? Is the slider manuel or vacuum controlled?
What's the vacuum actuated valve in the heater hose near the firewall all about? when is it activated?

Tomorrow I will try clamping the heater hose and see if that makes the AC cooler,meanwhile if someone can wise me up on how the whole system works it would be appreciated.

Cheers,

GDU.
 

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My understanding is the "AC" button should cause vacuum to be applied to the valve on the heater hose stopping the flow of hot coolant through the core. The "AC MAX" button does the same and additionally opens the recirc door by the passengers feet.

The valve on the heater hose are notorious for being stuck on older vehicles. with the truck running, hit the ac button and check for vacuum at the valve. if nothing, the HVAC vacuum system has an issue. if there is vacuum, the heater hose shutoff valve has an issue.
 

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The heat button is there to direct hot air to floor vents when pushed in.
The hot water shutoff valve receives vacuum only with selection of Max AC button. To check operation of hot water shutoff valve...with engine running,Max AC selected,remove vacuum hose from hot water shutoff valve. Observe action of lever on vacuum motor on valve. Lever should move to opposite position and return when hose reinstalled. If it does not,remove hose and check for vacuum with a gauge or your finger. If you have vacuum at hose and lever on valve does not move,either the diaphragm in vacuum motor is ruptured or the valve itself is seized possibly from corrosion
To determine which,you can manually work the lever back and forth. If it won't move,likely seized/corroded. It is a normally "open" valve and closes only with Max AC mode. If Ac has been inop for some time and or truck sat for a long time,it is possible valve is stuck open. You can clamp off heater hose with hose pinching pliers and start and run truck to check AC temp output at dash. Depending on what type of refrigerant your system was charged with,outlet temps in Max AC mode should be 45-55 degrees.

If there is no vacuum at shutoff valve,start tracing backwards into cab til find source. You can open glovebox door and pull all the way down and observe where vacuum tubing comes in thru firewall to be certain it's intact. Do Defrost,bilevel,heat modes all function properly? If air output does not switch with selection of all modes,likely same reason no vacuum available at hot water shutoff valve and next place to look is at the connector that mates all the HVAC vacuum motor tubing to the heater control assembly. These are known to disintegrate and crumble  with age and cause vacuum leaks that keep some or all HVAC modes from operating correctly.  You can look under dash at heater controls for this connector,sometimes easier to view with radio removed.

I had no Max AC function in my 84 Ramcharger and it was this crumbled connector that was the culprit.
 

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I’m not the OP but I have the same issue and man  oh man, how I wish I’d seen this thread before I spent $2500 on a new compressor only to find it’s still blowing lukkewarm air.  But now I know where to look to fix the problem!  Thanks y’all.
 

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click on to enlarge  besides the water valve inop , the other thing that happens the blend door gets jambed up with debris and the foam seals rot and fail to seal .. so if on A/C its hot , check the sliders door inside the box .
 

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howdy / first Gen is 1972 to 1980 ,second Gen is 1981 to 1993

1st Gen uses a cable to shut a heater valve off in the engine bay on the right side just in front of were the heater hoses go into the Cab

2nd Gen uses Vacuum like the diagram above in the same spot
 

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Gregdownunder
https://ramchargercentral.com/profile/?u=323298

howdy / please fill out your SIG that shows at the bottom of your posts with your truck info = it cuts down on the BS and and you recieve better answers because members dont hafta guess which year toyota you drive ???

NOTE / if you dont know howto fill out your SIG just ask me or a Mod for help ;)
 

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Greg,  what year/vehicle? Also, do you know the high and low side pressures on the system?
 

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Discussion Starter · #10 ·
All, excellent advice, much appreciated.
I will see what happened to the valve when I turn on the AC max and report back.
Could you please explain the pressures on the system? Would the tec have checked these?
I have also updated as suggested my profile to show year and model,83 Ram Royal SE 318 727


Thanks,

GDU.
 

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Gregdownunder said:
All, excellent advice, much appreciated.
I will see what happened to the valve when I turn on the AC max and report back.
Could you please explain the pressures on the system? Would the tec have checked these?
I have also updated as suggested my profile to show year and model,83 Ram Royal SE 318 727

Thanks,

GDU.
That is correct. There are typical air conditioning gauges that are used to check the system charge on the high and low side of the system. The lowest a temperature can go is determined by the low-side temperature. Sometimes a system is overcharged and the low-side temperature is too high leading to warmer-than-desired temps.

Also, it helps to direct diagnostics - if the low-side pressure is correct, then you know have a air blending problem where the cold air is mixed with warm air from elsewhere (the heater matrix or outside of the vehicle)
 

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Discussion Starter · #12 ·
OK Ill ask the tec.
Anyhow for the moment I've checked the operation of the valve.
Thing is, there is constant vacuum at the valve irrespective of AC on or not, and the lever on it moves in and out when you connect/disconnect vacuum,however hot water still appears to circulate as the pipes are hot.
Is it possible the lever moves but the gate is stuck?
All that said, the temp coming out of the vent is sitting at around 58F which while cool is not as cold as I would expect, and it does not change with hot water circulating (clamped) or not.

Now I should tell you Ive recently had all emmision stuff removed including a bunch of vacume hoses and have upgraded the carb to a 600 Holley.
It's possible we removed something we should not have.

At the moment there is a vacuum hose (Black plastic) comes off the manifold tree and disappears into a rubber grommet in the firewall.This same grommet has a grey plastic hose coming out which goes to the valve in question.

Also the wire (green /black) which runs from where the AC goes into the firewall along the back and into the main wireing loom has an orange connecter on it thats not connected to anything.
Ill attach pics which may clarify things.
Am I missing anything that should be there?


 

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The hoses will get hot, but with vacuum to the valve it shouldn't let it circulate into the heater core. The vacuum should only be going to the valve with the AC at MAX setting however. You may have a stuck controller in the dash. The black and grey hard vacuum lines are vacuum into the dash to power AC doors and the heater valve.

I would check the operation of the heater valve - means disconnecting it and seeing if opens/closes with vacuum to the connector.

temp of 58 isn't awful, but it should be about 40, so there is definite room for improvement.

Not sure what that connector is for, maybe one of the emissions timers. I'll defer that to one of the other guys here. It seems to go to one of the AC clutch switches but your AC works, so I don't know
 

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Discussion Starter · #14 ·
dodge82273 said:
click on to enlarge besides the water valve inop , the other thing that happens the blend door gets jambed up with debris and the foam seals rot and fail to seal .. so if on A/C its hot , check the sliders door inside the box .
Any chance you could copy and post the page next to this diagram?It looks like it explains how everything works which Im still a little hazy on.
I had a look behind the glovebox,the vacuum actuator towards the passenger door works fine when pushing various buttons,however the one closer to the center of the vehicle does not appear to work at all,so Im picking thats part of the problem.
I think I may have to remove to control unit and see if anything obvious is wrong there,any tips to removing it?

 

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one is a vac can ,the push buttons operate  the other the slider operates .  firewall vac lines are shown in the pix , push button switches the vac to the valve on/off . there is a clearish connector for the vac lines in dash about 3 inches from the push button cluster , that vac connector disintergrates over time , and falls apart .... small sections of windshield washer hose can be used to reconnect the cluster to the proper vac plastic lines ... I have drawn a diagram ( for myself/next time ) of the button cluster's operation/hose connections .. says 1987 , but like dodgeboys said ... 1981 on applies here ...  that water valve ? on/off stops hot water from goin to cab ... the colors of the lines in pix show where/when ( what button is selected/pushed) vac is applied there is 1 vac supply line from motor TO buttons , 1 from buttons to water valve ... read caption below pix ,( button selected) look at colored vac line ... 
 

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My 84 had issues with the HVAC controls /vacuum and taking apart and cleaning and lubing the switch made it operate much better. the vacuum slider gets dry and doesn't seal very well. the inline connector was also disintegrated. the other thing is make sure the check valve is in place and functional between the engine and HVAC. then your doors/valve should stay in place in low vacuum situations. having full vacuum to the system makes a big difference.
 
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