Chevy & GMC Vans

Anybody got any pic's of this culprit ??/ I thought I replaced all the vacuum lines in the A/C heater system when I noticed that that heater took a long time to get going and even then it wasn't close to being 170 degrees as to the new thermostat that I installed ??/ So thinking now it could either be the vacuum hose going to it or the control valve it self ?// Any pic's would be helpful as my Chiltons does not give a clue as to location and or vacuum hose routing ??/

Are you saying you installed a 170° thermostat? It's also possible there is still air in the system.

This is a good site for parts breakdowns: http://www.gmpartseast.com/Page_Product ... =53M&Year=

#20 / 21 is heater control valve, four and six port depending on if you have rear heat.

Stroverlander wrote:Are you saying you installed a 170° thermostat? It's also possible there is still air in the system.

This is a good site for parts breakdowns: http://www.gmpartseast.com/Page_Product ... =53M&Year=

#20 / 21 is heater control valve, four and six port depending on if you have rear heat.

Yah had to order it special from Auto Zone??/ Its also a fail safe ( Stays open if it fails ) In looking at your pic's your showing a 4 port valve and giving my Vin # to GMPatsgient.com mines calling for the 6 port valve ??/ I was thinking about removing the air assist valve and installing a ball valve ( keeps the heat away from the interior in the summer ) but now I don't no with it calling for a 6 port valve ??/ Have you got rear A/C and heat in your van ??/ It is the 4 port that you replaced isn't it ??/ Write back Steve

The 6 port is used if you have rear heat.

I would also check the vacuum line to the vacuum ball ( fig 34 ). Mine was rotted / leaking and may have been the cause of wild fluctuations in heat in my van last winter. In trying to get heat back I swapped the thermostat, waterpump ( cause I was in there ), and broke the 6 way valve before I found the rotted line. Heats been great since.

I believe that if the valve does not see vacuum it closes ( hence no heat when the vacuum line is broken ). Or if you have a vacuum leak it only opens partially so you have weak heat

howso48 wrote:Yah had to order it special from Auto Zone??/ Its also a fail safe ( Stays open if it fails ) In looking at your pic's your showing a 4 port valve and giving my Vin # to GMPatsgient.com mines calling for the 6 port valve ??/ I was thinking about removing the air assist valve and installing a ball valve ( keeps the heat away from the interior in the summer ) but now I don't no with it calling for a 6 port valve ??/ Have you got rear A/C and heat in your van ??/ It is the 4 port that you replaced isn't it ??/ Write back Steve

I only posted the 4 port to give you an idea what it looked like. Like Lifted said, rear heat = 6 port.

Good point by blacknome about checking the vacuum lines too, I replaced mine last year after I noticed they were looking cracked and collpased.

The give away on vacuum leak is often that you lose ventilation control in the cabin. Vents default to defrost position and will not switch to floor or front dash vents. If you are only getting heat and A/C through the dash defrost vents, definitely check all vacuum lines.

Any way did the less expensive mode first which was changing the thermostat first ??/ So removed the 170 degree that I special ordered ( MOTORad, @ Auto Zone ) as a fail safe 170 deg. got down to the neck and sure enough it was wide open ??/ 1 st clue there was no water in the hose when I disconnected it?// Second clue is I have no idea what temperature above 170 it was suppose to perform its fail safe function ??/ It could have been at 175 degrees for all I know??/ Anyway put the new AC DELCO down in ??/ After looking at it didn't have any of the fail safe features on it as the 170 deg. did and they sold it as a fail safe ??/ Got it back together and low and behold it works ??/ Heat for the winter ??/ Now all I have to wait for is the radiator to burp a couple of times and the system should be full capacity ??/