General Tech Help Good at troubleshooting? Have a non specific issue? Discuss general tech topics here...

91 mercury marquis heater/ac

  #1  
Old 01-19-2006, 09:37 PM
Junior Member
Thread Starter
Join Date: Jan 2006
Location: Canada
Posts: 2
Default

Why does the a/c blow cold until ,I come to a hill and then switches and blows heat. I know this must be a vacuum problem but don't know what to look for.Any help is appreciated.
 
  #2  
Old 01-20-2006, 11:09 PM
Junior Member
Join Date: Jan 2006
Location: United States
Posts: 11
Default

The control mechanism used to move or hold you airflow diveter doors is a small diaphragamvacuum motor. Usually one for each door. When you increase the load on the engine, and ther is wear on the postin rings, it can lose vacuum in the intake manifold. There is a vacuum canister(reservoir) in the engine compartment of the vehicle. It has enough volume to temporarily keep vacuum levels in the control system during loss of engine vacuum. Sounds like the internal check valve in the reservoir is leaking-common problems with age-- or you have a leak in the control system that allows loss of vacuum during periods of low engine vacuum. Check for loose vacuum connection at the rear of your control head assembly in the dash. then lool for loose fittings on any vacuum motors. Visually inspect all hoses for cracks or obvious deterioration. Hard lines crack with age and the rubber type lines can get soft and porous or develop cracks. Mightr want to check for manifold vacuum at the engine port when engine is idling. If you can get a vacuum gage, the engine should rpoduce a vacuum of approximately 14 to 18 inches of Hg at idle( throttle fully closed) and show less as the throttle is opened.
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Coodeville
Grand Marquis
0
11-28-2011 05:09 PM
Kojack
Sable
3
03-10-2011 03:00 AM
roaddogg
Grand Marquis
4
08-07-2006 01:03 PM
western
Tracer
3
02-23-2006 12:28 PM
scooter
General Tech Help
1
01-21-2006 01:14 AM


Thread Tools
Search this Thread
Quick Reply: 91 mercury marquis heater/ac


Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.