Door Lock Problem is Temp-related
 

Recently I fixed the bellows on two of my door lock actuators, and they seem to be holding up well. However, in colder weather, the car does not seem to hold vacuum. Either the check valve in the driver's door is bad or the culprit may be what appears to be an "extra" check valve on the middle line coming from the main valve. Refer to the pic below.

Note the big arrow pointing to the middle line, and the inline check valve. Is that supposed to be there? I referred to a diagram of the vacuum system in the driver's door, and this little bugger was not there. Perhaps the main valve was bleeding off vac, and this was installed in order to retain vacuum. Any ideas?

I guess I will attempt to remove it and see what happens, but I'm betting that my main valve (with the three lines feeding into it) is bad...

Mine do not have that extra check valve. The main vacuum supply line has a check valve installed on the "inside of the cabin" side of the firewall. If the check valve referred to in the above sentence goes bad I can understand why someone would put one in the location as you have shown.

I agree
 

I must agree with Jim on this. The check valve under the dash is VERY difficult to replace. I mine ever goes bad I will repair it in this fashion or some where else along the supply line that is easier to access.

thebern